Difference between revisions of "Why Were Nadav and Avihu Killed/2"

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<opinion>Breached Boundaries
 
<opinion>Breached Boundaries
 
<p>Nadav and Avihu overreached beyond what was permitted to them in approaching God.</p>
 
<p>Nadav and Avihu overreached beyond what was permitted to them in approaching God.</p>
 +
<mekorot><multilink><a href="SifraVayikra10-1" data-aht="source">Sifra Vayikra</a><a href="SifraVayikra10-1" data-aht="source">10:1</a><a href="Sifra Vayikra" data-aht="parshan">About the Sifra Vayikra</a></multilink>, opinions in <multilink><a href="VayikraRabbah20-8-10" data-aht="source">Vayikra Rabbah</a><a href="VayikraRabbah20-8-10" data-aht="source">20:8-10</a><a href="Vayikra Rabbah" data-aht="parshan">About Vayikra Rabbah</a></multilink>,&#160;<multilink><a href="PesiktaDeRavKahana26-4-9" data-aht="source">Pesikta DeRav Kahana</a><a href="PesiktaDeRavKahana26-4-9" data-aht="source">26:4-9</a><a href="Pesikta DeRav Kahana" data-aht="parshan">About Pesikta DeRav Kahana</a></multilink>, <multilink><a href="TanchumaBehaalotekha16" data-aht="source">Tanchuma</a><a href="TanchumaBehaalotekha16" data-aht="source">Behaalotekha 16</a><a href="Tanchuma" data-aht="parshan">About the Tanchuma</a></multilink>,&#160;<multilink><a href="TargumPseudo-JonathanShemot24-10-11" data-aht="source">Targum Pseudo-Jonathan</a><a href="TargumPseudo-JonathanShemot24-10-11" data-aht="source">Shemot 24:10-11</a><a href="Targum Pseudo-Jonathan" data-aht="parshan">About Targum Pseudo-Jonathan</a></multilink>,&#160;<multilink><a href="RashiShemot24-10" data-aht="source">Rashi</a><a href="RashiShemot24-10" data-aht="source">Shemot 24:10</a><a href="R. Shelomo Yitzchaki (Rashi)" data-aht="parshan">About R. Shelomo Yitzchaki</a></multilink>, <multilink><a href="AbarbanelVayikra10-1" data-aht="source">Abarbanel</a><a href="AbarbanelVayikra10-1" data-aht="source">Vayikra 10:1</a><a href="R. Yitzchak Abarbanel" data-aht="parshan">About R. Yitzchak Abarbanel</a></multilink>,<fn>Abarbanel points to several sins, one of which was entering the Holy of Holies.</fn></mekorot>
 
<point><b>Coming too close</b> – These sources all agree that Nadav and Avihu came too close to Hashem, but differ regarding the specific problematic action:<br/>
 
<point><b>Coming too close</b> – These sources all agree that Nadav and Avihu came too close to Hashem, but differ regarding the specific problematic action:<br/>
 
<ul>
 
<ul>
<li><b>Entered Holy of Holies</b> – One opinion in the Sifra, Bar Kappara in Vayikra Rabbah, and Abarbanel all fault Nadav and Avihu for bringing their offering into the Inner Sanctum which was forbidden to all but the high priest on the Day of Atonement. As this is where Hashem's presence is most strongly felt, unauthorized entry was not only prohibited but dangerous.</li>
+
<li><b>Entered Holy of Holies</b> – One opinion in the Sifra, Bar Kappara in Vayikra Rabbah, and Abarbanel all fault Nadav and Avihu for bringing their offering into the Inner Sanctum which was forbidden to all but the high priest on the Day of Atonement.&#160; As this is where Hashem's presence is most strongly felt, unauthorized entry was not only prohibited but dangerous.</li>
<li><b>Saw God</b> – One opinion in Vayikra Rabbah, Tanchuma, Targum Pseudo-Jonathon and Rashi assert that Nadav and Avihu were punished not for their actions on the eighth day, but for having seen God at Mount Sinai,<fn>Both Rashi and Targum Pseudo-Jonathan attribute more than one sin to Nadav and Avihu and might assume that they were punished for multiple actions.</fn> as described in Shemot 24.<fn>Rashi explains that Hashem waited to kill them because He did not want to turn the happiness of the day of receiving the Torah into a tragedy.&#160; It is not clear, however, why He would instead choose to kill them on the day of the Consecration of the Mishkan, a similarly happy occasion.</fn>&#160; One might similarly explain that the problem was seeing God on the eighth day itself; as God's presence had descended on the Tabernacle it is possible that the brothers encountered it upon entry into the Sanctuary.<fn>See Shemot 40:35, that when Hashem's glory filled the Tabernacle, even Moshe himself could not enter.</fn></li>
+
<li><b>Saw God</b> – One opinion in Vayikra Rabbah, Tanchuma, Targum Pseudo-Jonathon and Rashi assert, instead, that Nadav and Avihu were punished not for their actions on the eighth day, but for having seen God at Mount Sinai,<fn>Both Rashi and Targum Pseudo-Jonathan attribute more than one sin to Nadav and Avihu and might assume that they were punished for multiple actions.</fn> as described in <a href="Shemot24-9-11" data-aht="source">Shemot 24</a>.<fn>Rashi explains that Hashem waited to kill them because He did not want to turn the happiness of the day of receiving the Torah into a tragedy.&#160; It is not clear, however, why He would instead choose to kill them on the day of the Consecration of the Mishkan, a similarly happy occasion.</fn>&#160; One might similarly explain that the problem was seeing God on the eighth day itself; as God's presence had descended on the Tabernacle it is possible that the brothers encountered it upon entry into the Sanctuary.<fn>See Shemot 40:35, that when Hashem's glory filled the Tabernacle, even Moshe himself could not enter.</fn></li>
 +
</ul></point>
 +
<point><b>לִפְנֵי י"י</b> – Those who maintain that the brothers entered the Inner Sanctum point to this phrase as proof.&#160; "לִפְנֵי י"י" refers to the Holy of Holies, where Hashem's presence dwells.<fn>See Shemot 16:33-34 where the term "לִפְנֵי י"י" appears to be equated with "לִפְנֵי הָעֵדֻת", referring to the ark, and thus must refer to the Inner Sanctum.</fn>&#160; It is also possible that it refers even to the Outer Sanctuary, but due to Hashem's presence there, this too was forbidden.</point>
 +
<point><b>בְּקׇרְבָתָם לִפְנֵי י"י</b> – The description of the sin in&#160;<a href="Vayikra16-1-2" data-aht="source">Vayikra 16</a> as "when they came close to Hashem" might support this approach as it emphasizes this aspect.</point>
 +
<point><b>"אֵשׁ זָרָה"</b> – This phrase is difficult for this position since these sources posit that the problem was not in the offering itself.&#160; <br/>
 +
<ul>
 +
<li>Those who suggest that the sin occurred on the eighth day might suggest that since the brothers were unauthorized to enter the Inner Sanctum/Tabernacle, any offering they brought there would be considered "foreign".<fn></fn>&#160;</li>
 +
<li>Those who say that they were punished for seeing Hashem at Sinai might suggest instead that Nadav and Avihu did sin by bringing a foreign fire, yet this sin was not serious enough to warrant a punishment of death had it not been for their earlier actions.</li>
 +
</ul></point>
 +
<point><b>"אֲשֶׁר לֹא צִוָּה אֹתָם"</b> – This position might read this phrase as referring back to the term "וַיַּקְרִיבוּ לִפְנֵי י"י" rather than the term "אֵשׁ זָרָה".&#160; It was the coming close to Hashem that was not commanded.</point>
 +
<point><b>"הוּא אֲשֶׁר דִּבֶּר י"י לֵאמֹר בִּקְרֹבַי אֶקָּדֵשׁ"</b> – This position could explain this phrase to mean that Hashem had said "through those who come close, I will be consecrated".&#160;<multilink><a href="ChizkuniVayikra10-1-3" data-aht="source">Chizkuni</a><a href="ChizkuniVayikra10-1-3" data-aht="source">Vayikra 10:1-3</a><a href="R. Chizkiyah b. Manoach (Chizkuni)" data-aht="parshan">About R. Chizkiyah b. Manoach</a></multilink> asserts that the source of this statement is Hashem's words at Sinai, "וְגַם הַכֹּהֲנִים הַנִּגָּשִׁים אֶל י"י יִתְקַדָּשׁוּ".&#8206;<fn>In context the warning applies only to revelation and refers to proper preparations for those who were&#160; to approach Hashem, lest they be punished.</fn>&#8206;</point>
 +
<point><b>Severity of the punishment</b> – Those who assert that the brothers actually saw Hashem's presence can easily explain the brothers' death. This is the consequence of getting too close; as Hashem says, "לֹא יִרְאַנִי הָאָדָם וָחָי".&#160; Even just entering sacred space is a serious breach and deserves punishment, regardless of a person's motives.</point>
 +
<point><b>Biblical parallels</b> – Several stories in Tanakh show similar punishments for breach of boundaries:<br/>
 +
<ul>
 +
<li><b>Revelation at Sinai</b> – In <a href="Shemot19-12-1321-24" data-aht="source">Shemot 19</a>, Hashem repeatedly warns the nation not to get too close to the mountain, telling them "כׇּל הַנֹּגֵעַ בָּהָר מוֹת יוּמָת".</li>
 +
<li><b>Uzza</b> – In <a href="ShemuelII6-6-7" data-aht="source">Shemuel II 6</a>, Uzza touched the Ark to ensure that it did not fall.&#160; Despite his good intentions, his breaching of boundaries resulted in death.<fn>This chapter was likely chosen as the haftarah for Parashat Shemini due to the similarities between the stories. In both cases there is a celebration for a consecration of the Tabernacle/Ark in which an undefined sin relating to improper worship is punished by death. It is interesting to note that the name of Uzza's father is Avinadav, a combination of the names Nadav and Avihu.</fn></li>
 
</ul></point>
 
</ul></point>
<point><b>לִפְנֵי י"י</b> – Those who maintain that the brothers entered the Inner Sanctum, point to this phrase as proof.&#160; "לִפְנֵי י"י" refers to the Holy of Holies, where Hashem's presence is most felt.&#160; It is also possible that it only refers to the Outer Sanctuary, but due to Hashem's presence there, this too was forbidden.</point>
 
<point><b>בְּקׇרְבָתָם לִפְנֵי י"י</b> – The description of the sin in Vayikra 16 as "when they came close to Hashem" might support this approach, as it emphasizes this aspect.</point>
 
<point><b>"אֵשׁ זָרָה"</b> – This phrase is difficult for this position since these sources posit that the problem is not in the offering itself.&#160; They might claim that the phrase means an unauthorized offering, which was not commanded and therefore should not have been brought, but which in and of itself would not have caused their deaths.</point>
 
<point><b>"הוּא אֲשֶׁר דִּבֶּר י"י לֵאמֹר בִּקְרֹבַי אֶקָּדֵשׁ"</b> – This position could explain this phrase to mean that Hashem had said "those who come close will be consecrated". Chizkuni asserts that the source of this statement is Hashem's words at Sinai, "וְגַם הַכֹּהֲנִים הַנִּגָּשִׁים אֶל י"י יִתְקַדָּשׁוּ".&#8206;<fn>In context the warning applies only to revelation and refers to proper preparations for those who were&#160; to approach Hashem, lest they be punished.</fn>&#8206;</point>
 
 
</opinion>
 
</opinion>
 
<opinion>Breached Boundaries
 
<opinion>Breached Boundaries
Line 64: Line 76:
 
<point><b>Biblical parallels</b> – Several stories in Tanakh show similar punishments for breach of boundaries:<br/>
 
<point><b>Biblical parallels</b> – Several stories in Tanakh show similar punishments for breach of boundaries:<br/>
 
<ul>
 
<ul>
<li><b>Revelation at Sinai</b> – In <a href="Shemot19-12-1321-24" data-aht="source">Shemot 19</a>, Hashem repeatedly warns the nation not to get too close to the mountain, telling them "כׇּל הַנֹּגֵעַ בָּהָר מוֹת יוּמָת".</li>
 
 
<li><b>Korach</b> – In the story of Korach, unauthorized incense offerings result in death.</li>
 
<li><b>Korach</b> – In the story of Korach, unauthorized incense offerings result in death.</li>
 +
<li>Revelation at Sinai – In <a href="Shemot19-12-1321-24" data-aht="source">Shemot 19</a>, Hashem repeatedly warns the nation not to get too close to the mountain, telling them "כׇּל הַנֹּגֵעַ בָּהָר מוֹת יוּמָת".</li>
 
<li><b>Uzza</b> – In <a href="ShemuelII6-6-7" data-aht="source">Shemuel II 6</a>, Uzza touched the Ark to ensure that it did not fall.&#160; Despite his good intentions, his breaching of boundaries resulted in death.<fn>This chapter was likely chosen as the haftarah for Parashat Shemini due to the similarities between the stories.&#160; In both cases there is a celebration for a consecration of the Tabernacle/Ark in which an undefined sin relating to improper worship is punished by death.&#160; It is interesting to note that the name of Uzza's father is Avinadav, a combination of the names Nadav and Avihu.</fn></li>
 
<li><b>Uzza</b> – In <a href="ShemuelII6-6-7" data-aht="source">Shemuel II 6</a>, Uzza touched the Ark to ensure that it did not fall.&#160; Despite his good intentions, his breaching of boundaries resulted in death.<fn>This chapter was likely chosen as the haftarah for Parashat Shemini due to the similarities between the stories.&#160; In both cases there is a celebration for a consecration of the Tabernacle/Ark in which an undefined sin relating to improper worship is punished by death.&#160; It is interesting to note that the name of Uzza's father is Avinadav, a combination of the names Nadav and Avihu.</fn></li>
 
</ul></point>
 
</ul></point>

Version as of 00:34, 1 April 2016

Why Were Nadav and Avihu Killed?

Exegetical Approaches

This topic has not yet undergone editorial review

Punished for Sin

Nadav and Avihu were killed as part of a Divine punishment for a sin.

Breached Boundaries

Nadav and Avihu overreached beyond what was permitted to them in approaching God.

Coming too close – These sources all agree that Nadav and Avihu came too close to Hashem, but differ regarding the specific problematic action:
  • Entered Holy of Holies – One opinion in the Sifra, Bar Kappara in Vayikra Rabbah, and Abarbanel all fault Nadav and Avihu for bringing their offering into the Inner Sanctum which was forbidden to all but the high priest on the Day of Atonement.  As this is where Hashem's presence is most strongly felt, unauthorized entry was not only prohibited but dangerous.
  • Saw God – One opinion in Vayikra Rabbah, Tanchuma, Targum Pseudo-Jonathon and Rashi assert, instead, that Nadav and Avihu were punished not for their actions on the eighth day, but for having seen God at Mount Sinai,2 as described in Shemot 24.3  One might similarly explain that the problem was seeing God on the eighth day itself; as God's presence had descended on the Tabernacle it is possible that the brothers encountered it upon entry into the Sanctuary.4
לִפְנֵי י"י – Those who maintain that the brothers entered the Inner Sanctum point to this phrase as proof.  "לִפְנֵי י"י" refers to the Holy of Holies, where Hashem's presence dwells.5  It is also possible that it refers even to the Outer Sanctuary, but due to Hashem's presence there, this too was forbidden.
בְּקׇרְבָתָם לִפְנֵי י"י – The description of the sin in Vayikra 16 as "when they came close to Hashem" might support this approach as it emphasizes this aspect.
"אֵשׁ זָרָה" – This phrase is difficult for this position since these sources posit that the problem was not in the offering itself. 
  • Those who suggest that the sin occurred on the eighth day might suggest that since the brothers were unauthorized to enter the Inner Sanctum/Tabernacle, any offering they brought there would be considered "foreign".6 
  • Those who say that they were punished for seeing Hashem at Sinai might suggest instead that Nadav and Avihu did sin by bringing a foreign fire, yet this sin was not serious enough to warrant a punishment of death had it not been for their earlier actions.
"אֲשֶׁר לֹא צִוָּה אֹתָם" – This position might read this phrase as referring back to the term "וַיַּקְרִיבוּ לִפְנֵי י"י" rather than the term "אֵשׁ זָרָה".  It was the coming close to Hashem that was not commanded.
"הוּא אֲשֶׁר דִּבֶּר י"י לֵאמֹר בִּקְרֹבַי אֶקָּדֵשׁ" – This position could explain this phrase to mean that Hashem had said "through those who come close, I will be consecrated". ChizkuniVayikra 10:1-3About R. Chizkiyah b. Manoach asserts that the source of this statement is Hashem's words at Sinai, "וְגַם הַכֹּהֲנִים הַנִּגָּשִׁים אֶל י"י יִתְקַדָּשׁוּ".‎7
Severity of the punishment – Those who assert that the brothers actually saw Hashem's presence can easily explain the brothers' death. This is the consequence of getting too close; as Hashem says, "לֹא יִרְאַנִי הָאָדָם וָחָי".  Even just entering sacred space is a serious breach and deserves punishment, regardless of a person's motives.
Biblical parallels – Several stories in Tanakh show similar punishments for breach of boundaries:
  • Revelation at Sinai – In Shemot 19, Hashem repeatedly warns the nation not to get too close to the mountain, telling them "כׇּל הַנֹּגֵעַ בָּהָר מוֹת יוּמָת".
  • Uzza – In Shemuel II 6, Uzza touched the Ark to ensure that it did not fall.  Despite his good intentions, his breaching of boundaries resulted in death.8

Breached Boundaries

Nadav and Avihu overreached beyond what was permitted to them in approaching God.

What boundaries were breached? These sources maintain that the brothers erred in bringing an incense offering that they were not authorized to bring, and/or that they came too close to God:
  •  Unauthorized offering – The sources differ regarding the problem:
    • Extra incense – Many of these sources9 explains that the brothers voluntarily brought their own individual incense offering.10 Since the verse states that "לֹא תַעֲלוּ עָלָיו קְטֹרֶת זָרָה", any extra incense offering was considered problematic.11
    • Took Aharon's job – Abarbanel, instead, explains that the brothers were unauthorized because on the eighth day Aharon alone was supposed to do all aspects of the service,12 similar to rituals of the Day of Atonement which are done by the high priest alone.13  Seforno goes further to suggest that throughout the period of Wanderings in the Wilderness only the high priest was allowed to bring incense (or perform any other services in the sanctuary) due to Hashem's constant presence on the Tabernacle.14 
  • Coming too close – Commentators elaborate on this in two ways:
    • Entered Holy of Holies – One opinion in the Sifra, Bar Kappara in Vayikra Rabbah, and Abarbanel all fault Nadav and Avihu for bringing their offering into the Inner Sanctum which was forbidden to all but the high priest on the Day of Atonement.  As this is where Hashem's presence is most strongly felt, unauthorized entry was not only prohibited but dangerous. 
    • Saw God – One opinion in Vayikra Rabbah, Tanchuma, Targum Pseudo-Jonathon and Rashi assert that Nadav and Avihu were punished not for their actions on the eighth day, but for having seen God at Mount Sinai,15 as described in Shemot 24.16  One might similarly explain that the problem was seeing God on the eighth day itself; as God's presence had descended on the Tabernacle it is possible that the brothers encountered it upon entry into the Sanctuary.17
"אֵשׁ זָרָה" – According to these sources, this phrase is equivalent to "קְטֹרֶת זָרָה", meaning an unauthorized incense offering.  The Biur explains that the term "אֵשׁ" is really just a variation of the term "אִשֶּׁה לַי"י'‏", another name for sacrifices.18
"לִפְנֵי י"י" – According to many of these sources,19 the phrase refers to the Holy of Holies, the forbidden Inner Sanctum.
"בְּקׇרְבָתָם לִפְנֵי י"י" – The description of the sin in Vayikra 16 as "when they came close to Hashem" might support this approach, as it emphasizes this aspect.
"אֲשֶׁר לֹא צִוָּה אֹתָם"
  • Not commanded – According to most of these sources the fact that the incense offering was not commanded is what made it foreign, and therefore problematic. R. Hirsch emphasizes how there is no such thing as subjectivity in sacrificial service; a person cannot act on their own individual desires, but only on the commands of Hashem.20
  • Prohibited – Chizkuni instead reads the verse to mean "which Hashem commanded not [to bring]", pointing to the prohibition in Shemot 30:9 against bringing a "foreign incense offering".  The brothers were violating an explicit command, and therefore punished.
What motivated the brothers?
  • Zeal for Hashem – According to the Biur, R. Hirsch and R. D"Z Hoffmann the brothers' motivations were pure. They brought the sacrifice out of a desire for closeness to Hashem.21
  • Mistaken – Seforno suggests that Nadav and Avihu mistakenly assumed that just like an incense is burned after the Daily Offering due to its bringing of Hashem's presence, so too after Hashem's fire descended and His glory was revealed, an incense offering was called for.22
  • Honoring their father – Hoil Moshe suggests that the brothers were worried about their father's honor.  Seeing that Hashem's glory descended only after Moshe came to the Tabernacle to pray, they thought that others would think that their father was unworthy to brings God's presence.23  As such, they thought to bring an incense to prove that their immediate family, too, was desired by God.
  • Arrogance – Shadal, in contrast, attributes the brothers' actions to excessive haughtiness and a desire not to be overshadowed by their father.24 Since they had not been given any individual service to perform they took upon themselves one of the most precious rituals.
"הוּא אֲשֶׁר דִּבֶּר י"י לֵאמֹר בִּקְרֹבַי אֶקָּדֵשׁ"
  • This position could explain this phrase to mean that Hashem had said "those who come close will be consecrated". Chizkuni asserts that the source of this statement is Hashem's words at Sinai, "וְגַם הַכֹּהֲנִים הַנִּגָּשִׁים אֶל י"י יִתְקַדָּשׁוּ".‎25
  • According to the Biur, R. Hirsch and R. D"Z Hoffman, Moshe comforted Aharon in these words, telling him that his sons were among Hashem's most holy. Though their actions were wrong, they were motivated by a closeness to God, and not sinful thoughts.26
Severity of the punishment
  • Those who assert that the brothers actually saw Hashem's presence can easily explain the brothers' death. This is the consequence of getting too close; as Hashem says, "לֹא יִרְאַנִי הָאָדָם וָחָי".  It is possible that even just entering sacred space is a serious breach and deserves punishment, regardless of a person's motives.27
  • Those who view the sin as relating only to an unauthorized incense might also view it as a serious sin, especially since a "קְטֹרֶת זָרָה" is explicitly prohibited. The Biur, R. Hirsch, and the Hoil Moshe, nonetheless, assert that the brothers were only punished so severely due to their high stature.  The Biur compares their punishment to that of Moshe and Aharon by the rock, whose sin merited disproportionately severe consequences. He notes that there too the verse states "וַיִּקָּדֵשׁ בָּם".‎28 
Biblical parallels – Several stories in Tanakh show similar punishments for breach of boundaries:
  • Korach – In the story of Korach, unauthorized incense offerings result in death.
  • Revelation at Sinai – In Shemot 19, Hashem repeatedly warns the nation not to get too close to the mountain, telling them "כׇּל הַנֹּגֵעַ בָּהָר מוֹת יוּמָת".
  • Uzza – In Shemuel II 6, Uzza touched the Ark to ensure that it did not fall.  Despite his good intentions, his breaching of boundaries resulted in death.29
The Yom HaKippurim Service – The verses that describe the service of the Day of Atonement clearly connect it to the deaths of Nadav and Avihu.  Hoil Moshe asserts that the entire service was necessary to cleanse the Inner Sanctum from the impurity caused by the deaths of Nadav and Avihu.  Alternatively, the directives might be coming to prevent a repeat of the sin, teaching Aharon the proper protocol to safely enter the Inner Sanctuary.

Problematic Procedure

Nadav and Avihu violated proper protocol when bringing the incense offering.

What was their transgression? These sources bring an array of possible wrongdoings including: bringing the wrong fire,30 not wearing the proper clothing, failing to wash before service, or entering the Mishkan while intoxicated.31  Though there is mention of the first wrongdoing, "וַיַּקְרִיבוּ לִפְנֵי י"י אֵשׁ זָרָה", there is no explicit mention of any of the other three.  Nonetheless, the fact that the prohibition to drink wine immediately follows the story might be brought as support that the crime involved drinking.
"אֵשׁ זָרָה"
  • Wrong fire – According to most of these commentators, this phrase describes Nadav and Avihu's main sin, bringing fire from a foreign source.  According to R. Yosef Bekhor Shor, although a priest is normally allowed to bring fire of his own ("מן ההדיוט"),‎32‎‎ on this day, Hashem had wanted the sacrifices to be consumed only via His fire33 so as to glorify His name.34  Alternatively the fire for the incense offering must always be brought from the Altar (as per Vayikra 16:12),35 but Nadav and Avihu brought it from a regular oven.36
  • Problematic offering –The sources who point to other procedural mistakes as the problem might suggest that any sacrifice not brought according to proper protocol is in essence a "foreign fire".
"אֲשֶׁר לֹא צִוָּה אֹתָם" – These commentators can explain this verse in one of two ways, depending on the sin attributed to Nadav and Avihu:
  • Lack of command – Ibn Ezra explains that the verse teaches that the brothers acted according to their own understanding, rather than on Hashem's command. Though Hashem had never prohibited Nadav and Avihu from bringing their own fire on the eighth day, He had not authorized it either.37
  • Prohibition – Those commentators who posit that the sin related to clothing, washing or drunkenness might instead explain the verse as if written,"אשר צוה אותם לא"‎38 ("that he commanded not to").  For each of these actions there is an explicit warning in Torah, and as such Nadav and Avihu should have known better.39 
" לִפְנֵי י"י" – Most of these sources would likely explain that "לִפְנֵי י"י" refers to the Outer Sanctum where the brothers brought the incense on the altar.40
What motivated the brothers?
  • Lack of faith – One opinion in the Sifra41 states that when the brothers saw that Aharon had finished his service but Hashem's presence had not descended, they worried and decided to bring fire of their own to help it along.42  Though their intentions were positive, their actions suggested a lack of faith and led to a lessening of God's glory.43
  • Mistake –  According to R"Y Bekhor Shor, Nadav and Avihu simply made a mistake, not realizing that Hashem did not want them to bring of their own fire on this day.44  Other procedural sins might similarly be explained as mistakes; the brothers were still new to service and might have erred in certain aspects. 
  • Carelessness – It is also possible that the brothers were simply careless, not giving Hashem's service the attention to detail it deserved. 
  • Surrounding influences – Alternatively, they might have been influenced by surrounding modes of worship.  Thus, for example, if others worshiped their gods while in a drunken frenzy, Nadav and Avihu might have thought to worship Hashem similarly.  This, though, brings worship of Hashem close to idolatry.45
"בִּקְרֹבַי אֶקָּדֵשׁ "
  • The brothers – R. Yosef Bekhor Shor46 asserts that the term "קְרֹבַי" refers to Nadav and Avihu, who, despite their error, were still considered close to Hashem.  Hashem was sanctified through them since the nation realized that if such holy individuals could be punished, they certainly needed to be careful in observance to evade punishment.
  • Aharon – Those who read the brothers less positively might explain, as does RashbamVayikra 10:1-3About R. Shemuel b. Meir, that the term refers not to Nadav and Avihu, but to Aharon, who was to sanctify Hashem's name by continuing with Hashem's service and not mourning.47
Severity of Punishment
  • Capital crimes – Those who maintain that the sin related to drinking, clothing or washing, can easily explain the severity of the punishment since all these sins are punishable by death.  Even if the brothers' motives were not negative, they nonetheless committed capital crimes.
  • Lesson to others –  Those who assert that the sin was bringing a foreign fire that was simply "not commanded" have a harder time explaining the punishment.  R"Y Bekhor Shor and Ralbag maintains that it needed to be severe to teach the nation the importance of being exacting in observing the laws of sacrifices. Seeing how Hashem punished even those who were close to him, taught laymen how much more they needed to fear God.
Context – prohibition to drink wine – According to this approach, the prohibition to drink wine might follow this story either because the brothers sinned in this regard, or simply as another warning of the need to be exacting and careful (and thus unimpaired by drink) when serving in the Mikdash.

Vicarious Punishment

Aharon's sons died, not for their own crimes, but as a punishment to Aharon for his participation in the Sin of the Golden Calf.

Sins of the father – This approach maintains that sometimes Hashem punishes children for their parent's sins. Thus, even though it was Aharon who sinned, it was his children who were killed. For a full discussion of the issue and how to explain the phenomenon, see Are Children Punished for Parents' Sins?
Why now? Or HaChayyim It is possible that before Aharon could fully serve in the Mishkan, his previous sins needed to be atoned and punished.
הוּא אֲשֶׁר דִּבֶּר י"י לֵאמֹר בִּקְרֹבַי אֶקָּדֵשׁ – Rashi claims that Hashem said this when He first relayed the commands regarding the consecration of the Tabernacle in Shemot 29,49 saying: "וְנֹעַדְתִּי שָׁמָּה לִבְנֵי יִשְׂרָאֵל וְנִקְדַּשׁ בִּכְבֹדִי".‎50  Though at that point the brothers had not yet done anything at all blameworthy, their deaths could already be decreed, since they were a punishment for the earlier act of Aharon.  As they themselves were innocent the brothers are called "קְרֹבַי".
Severity of the punishment – Since Aharon's actions led others to worship the Calf, a harsh punishment would seem warranted.  For a discussion of Aharon's actions and the nature of the Sin of the Golden Calf, see Sin of the Golden Calf
"וַיַּקְרִיבוּ לִפְנֵי י"י אֵשׁ זָרָה אֲשֶׁר לֹא צִוָּה אֹתָם" – This approach must explain why the verses suggest that Nadav and Avihu themselves erred, if they did nothing wrong.  It might explain that the brothers did mistakenly bring a foreign fire, but since this was not prohibited (simply not commanded) it would not have been considered a capital crime were it not that Hashem wanted to punish their father.
"לִפְנֵי י"י" – This approach would probably understand this to refer to the Outer Sanctum, where the brothers were permitted to enter.
"וַיִּדֹּם אַהֲרֹן" – This approach might explain that Aharon was silent, recognizing that the decree was his fault.

Work Accident

Nadav and Avihu's actions alone would not have warranted their death, but their being in the wrong place at the wrong time caused them to be consumed by Hashem's fire.

Order of the verses – Rashbam posits that the story of Nadav and Avihu really occurred before Hashem's fire consumed Aharon's offerings as described in Vayikra 9:24.  It is on this backdrop that he explains the rest of the story.
The incense offering – According to Rashbam, Nadav and Avihu were not bringing an unauthorized incense, but the regular offering brought every morning.
"אֵשׁ זָרָה" – The brothers' only mistake was in bringing "foreign fire" rather than waiting for Godly fire to consume the incense.  Rashbam explains that although a priest is normally allowed to bring fire of his own ("אש מן ההדיוט"),‎ during the Mishkan's consecration, Hashem had wanted to glorify His name by having all sacrifices be consumed via Hashem's fire.  R. Granot suggests, instead, that the brothers were impatient for Hashem's revelation and tried to "hurry the end".
"אֲשֶׁר לֹא צִוָּה אֹתָם" – Rashbam explains that although normally the brothers' actions would have been permitted, on this day, Hashem did not command them to do so.  As such, Nadav and Avihu had no way of knowing that their actions were not desired.
"וַתֵּצֵא אֵשׁ מִלִּפְנֵי י"י" – Rashbam identifies this fire with that described in Vayikra 9:24.53 The fire that consumed Aharon's offerings on Mizbach Ha'Olah was the same fire that killed the brothers.54  This fire emanated from "before God", from the Inner Sanctum, where Hashem's presence dwells.  As such, the godly fire did not come vertically down from the heavens, but traveled horizontally from the Holy of Holes to the Outer Sanctum (where it met the brothers) to the Copper Altar.
Severity of the punishment – According to this approach, the fire that killed Nadav and Avihu was not intended to punish them but simply to consume Aharon's sacrifices.  They, unfortunately, happened to be in the way and suffered the natural consequences.  In R. Granot's words, "their death was not a punishment but a tragic accident."
Why not bring the fire later? This approach must contend with the question of why Hashem allowed such an accident, rather than waiting to bring the fire when no one was in the way.  It could answer that since the brothers had sinned, albeit erroneously, they were not worthy of a miracle to save them. Alternatively, since the entire nation was outside waiting for Hashem's glory to appear there would be a huge desecration of His name if there were a delay.
"בִּקְרֹבַי אֶקָּדֵשׁ" – According to this approach it is understandable that the brothers are referred to as "close to Hashem" since they died without major sin.55
Biblical parallels – Other catastrophes in Tanakh have similarly been viewed as natural consequences rather than punishments. For example, see Mystery at the Malon for Abarbanel's reading of Moshe's near death being the result of lack of preparation for prophecy.  Netziv similarly explains the death of the "Maapilim" in Bemidbar 14 not as a punishment, but the natural result of war.

Sanctified to God

Nadav and Avihu's deaths were not a punishment but rather a sanctifying of their souls to Hashem.

Sources:PhiloOn Dreams 2:67On Flight and Finding, 59About Philo, perhaps HaKetav VeHaKabbalah
"בִּקְרֹבַי אֶקָּדֵשׁ" – This approach rests on the understanding that this phrase refers to Nadav and Avihu who are described as "close to Hashem".  If they are referred to as such in death, it is not possible that their actions were seen as sinful in the eyes of Hashem.  Moreover, if their death served to sanctify Hashem, it must not have been a punishment but some sort of elevation.
"וַיַּקְרִיבוּ... אֵשׁ זָרָה אֲשֶׁר לֹא צִוָּה אֹתָם"
  • Philo reads this fire metaphorically to refer to the passion of Nadav and Avihu's love for God which they offered up to Him with their whole being.  It is referred to as a "foreign" fire because it was "foreign to earthly existence since it belonged to the realm of God".
  • More simply, the verse could mean that Nadav and Avihu offered a non-obligatory sacrifice.  It was called foreign because it had not been commanded.  According to this reading, the phrase "אֲשֶׁר לֹא צִוָּה אֹתָם" comes to explain the term "אֵשׁ זָרָה". It does not have a negative connotation, but rather comes to highlight the brothers' desire to give even more to Hashem than He obligated.
"לִפְנֵי י"י" – This position might explain the threefold repetition of the phrase "לִפְנֵי י"י" as coming to emphasize the brothers' desire to come close to Hashem and be before Him.
What motivated the brothers? HaKetav VeHaKabbalah quotes the Sifra that "כיון שראו אש חדשה... עמדו להוסיף אהבה על אהבה".  Upon seeing Hashem's presence and fire descend they felt a need to reciprocate and offer something up to Him in return.
Death is not always punishment – Philo compares the brothers' death to a "whole burnt offering" which rises heavenwards.  According to him, in the brother's desire for closeness, death would not have been viewed as a punishment but as a sanctification of their being to God.
Biblical parallels – This approach might compare Nadav and Avihu to Chanokh, whom Hashem "took" because he "walked with God".  [See Bereshit 5:24: "וַיִּתְהַלֵּךְ חֲנוֹךְ אֶת הָאֱלֹהִים וְאֵינֶנּוּ כִּי לָקַח אֹתוֹ אֱלֹהִים"].  In neither case should death be viewed negatively.  Rather, due to their extreme righteousness, sometimes loved ones are taken to be with Hashem earlier.
"וַתֹּאכַל אוֹתָם" – HaKetav VeHaKabbalah points out that since the verse states that Nadav and Avihu died, the phrase "and it consumed them" must come to teach something beyond the fact of their death.56 He suggests that the choice of verb connotes an acceptance of something with joy, and refers to the fact that Hashem accepted the brothers' souls with joy.