Ages of Levite Workers

Introduction

A Three Way Contradiction

Bemidbar 4 describes the census of the Levites who were to serve in the Mishkan,  repeating seven distinct times¹ that those aged 30-50 will participate in this national service:

EN/HEע/E

(ג) מִבֶּן שְׁלֹשִׁים שָׁנָה וָמַעְלָה וְעַד בֶּן חֲמִשִּׁים שָׁנָה כׇּל הַבָּא לַעֲבֹד עֲבֹדַת עֲבֹדָה וַעֲבֹדַת מַשָּׂא בְּאֹהֶל מוֹעֵד.

(3) from thirty years old and upward even to fifty years old, everyone who entered in to do the work of service, and the work of bearing burdens in the Tent of Meeting,

Somewhat surprisingly, just a few chapters later, in the context of the description of the consecration of the Levites in Bemidbar 8, a different age range is presented:

EN/HEע/E

(כד) זֹאת אֲשֶׁר לַלְוִיִּם מִבֶּן חָמֵשׁ וְעֶשְׂרִים שָׁנָה וָמַעְלָה יָבוֹא לִצְבֹא צָבָא בַּעֲבֹדַת אֹהֶל מוֹעֵד. (כה) וּמִבֶּן חֲמִשִּׁים שָׁנָה יָשׁוּב מִצְּבָא הָעֲבֹדָה וְלֹא יַעֲבֹד עוֹד. (כו) וְשֵׁרֵת אֶת אֶחָיו בְּאֹהֶל מוֹעֵד לִשְׁמֹר מִשְׁמֶרֶת וַעֲבֹדָה לֹא יַעֲבֹד כָּכָה תַּעֲשֶׂה לַלְוִיִּם בְּמִשְׁמְרֹתָם.

(24) “This is that which belongs to the Levites: from twenty-five years old and upward they shall go in to wait on the service in the work of the Tent of Meeting; (25) and from the age of fifty years they shall cease waiting on the work, and shall serve no more, (26) but shall minister with their brothers in the Tent of Meeting, to perform the duty, and shall do no service. You shall do thus to the Levites concerning their duties.”

These verses set twenty-five rather than thirty as the lower age limit.² How is the seeming contradiction to be understood?  Do the two chapters speak of different circumstances? 

Verses from Nakh add to the confusion.  From these verses it appears that, in the eras of David (Divrei HaYamim I 23:24-28), Chizkiyahu (Divrei HaYamim II 31:17), and Ezra (Ezra 3:8-11), the Levites began working already at the age of twenty!³  Did the law change from the period of the Wilderness and Tabernacle to the period of the Mikdash?  If so, what made the change necessary, who initiated it, and by what right?

Additional Questions

The terms used to describe the various functions of the Levites are somewhat ambiguous in meaning. Varying explanations of each might shed light on the questions above.

• "לִצְבֹא צָבָא" – When describing the Levites' tasks, the verses state  "כׇּל הַבָּא לַצָּבָא / לִצְבֹא צָבָא לַעֲבֹד עֲבֹדָה".‎⁴  What does this term mean?
• "כׇּל הַבָּא לַעֲבֹד עֲבֹדַת עֲבֹדָה וַעֲבֹדַת מַשָּׂא" –  The summary statement in Bemidbar 4 speaks of both "עֲבֹדַת עֲבֹדָה" and "עֲבֹדַת מַשָּׂא". What type of work is included in each of these phrases?  Neither of these terms is mentioned in Bemidbar 8; is this significant?
• "לְנַצֵּחַ עַל מְלֶאכֶת בֵּית י״י"–  In Ezra 3:9 and Divrei HaYamim I 23:4 a new term is used to describe the Levites' tasks, "לְנַצֵּחַ עַל מְלֶאכֶת בֵּית י״י".  What does "לְנַצֵּחַ" mean and what does this job entail? Is this a new job relevant only to work in the Mikdash and not the Mishkan?
• Post fifty – Which of their functions did the Levites no longer perform during their semi-retirement at age fifty? Which tasks did they maintain, and what jobs, if any, did they first assume? How did the Levites' non-work status after the age of fifty compare to that before the age of thirty?

¹ See Bemidbar 4:3, 23, 30, 35, 39, 43, and 47.

² The difference between the two chapters is highlighted by the Septuagint's translation of Chapter 4.  Throughout the chapter it consistently translates, "from twenty-five years old and upwards until fifty years" rather than "from thirty years", eliminating any contradiction with Chapter 8.

³ The textual difficulty is highlighted when one looks at Targum Yerushalmi (Neofiti) on Bemidbar 8:24.  It harmonizes the two sets of verses, setting the lower age limit in Bemidbar 8 as "twenty years of age", just as stated in the verses in Ezra and Divrei HaYamim.

⁴ See Bemidbar 4:23, 30, 35, 39, 43, and 8:24.