How Could She?
Chapter 2 of the Megillah describes how Esther was chosen to replace Vashti as Achashverosh's wife:
(טז) וַתִּלָּקַח אֶסְתֵּר אֶל הַמֶּלֶךְ אֲחַשְׁוֵרוֹשׁ אֶל בֵּית מַלְכוּתוֹ בַּחֹדֶשׁ הָעֲשִׂירִי הוּא חֹדֶשׁ טֵבֵת בִּשְׁנַת שֶׁבַע לְמַלְכוּתוֹ. (יז) וַיֶּאֱהַב הַמֶּלֶךְ אֶת אֶסְתֵּר מִכׇּל הַנָּשִׁים וַתִּשָּׂא חֵן וָחֶסֶד לְפָנָיו מִכׇּל הַבְּתוּלוֹת וַיָּשֶׂם כֶּתֶר מַלְכוּת בְּרֹאשָׁהּ וַיַּמְלִיכֶהָ תַּחַת וַשְׁתִּי.
(16) So Esther was taken unto king Ahasuerus into his house royal in the tenth month, which is the month Tebeth, in the seventh year of his reign. (17) And the king loved Esther above all the women, and she obtained grace and favour in his sight more than all the virgins; so that he set the royal crown upon her head, and made her queen instead of Vashti.
The marriage has bothered many readers of the Megillah. How could Esther marry a heathen? Why did neither she nor Mordechai protest her being taken? In the words of R. Saadia Gaon:
It is necessary for us to understand why Mordecai did not resist (the removal of) Esther to Achashverosh's palace, since it is clearly stipulated in the Torah, "Do not give your daughter to his son or take his daughter for your son" (Deut 7:3). Though we might aver that he was absolved from guilt because he was forced, according to our Oral Law the use of force does not in fact absolve one from guilt in connection with the three sins of idolatry, sexual immorality, and the shedding of innocent blood.
R. Saadia's question is based on two assumptions:
1) Marriage to an idolater is a cardinal sin for which one is obligated to sacrifice one's life.
2) Mordechai and Esther were Torah observant Jews who would have been bothered by such a transgression.
Each of these assumptions, however, requires further exploration.
Gravity of the Sin
The degree of severity of the sin in marrying Achashverosh is unclear. The Torah's prohibition of intermarriage can be found in Devarim Chapter 7:
(א) כִּי יְבִיאֲךָ י"י אֱ-לֹהֶיךָ אֶל הָאָרֶץ אֲשֶׁר אַתָּה בָא שָׁמָּה לְרִשְׁתָּהּ וְנָשַׁל גּוֹיִם רַבִּים מִפָּנֶיךָ הַחִתִּי וְהַגִּרְגָּשִׁי וְהָאֱמֹרִי וְהַכְּנַעֲנִי וְהַפְּרִזִּי וְהַחִוִּי וְהַיְבוּסִי שִׁבְעָה גוֹיִם רַבִּים וַעֲצוּמִים מִמֶּךָּ....
(ג) וְלֹא תִתְחַתֵּן בָּם בִּתְּךָ לֹא תִתֵּן לִבְנוֹ וּבִתּוֹ לֹא תִקַּח לִבְנֶךָ. (ד) כִּי יָסִיר אֶת בִּנְךָ מֵאַחֲרַי וְעָבְדוּ אֱלֹהִים אֲחֵרִים וְחָרָה אַף י"י בָּכֶם וְהִשְׁמִידְךָ מַהֵר.
And you shall not marry into them, your daughter you shall not give to his son, and his daughter you shall not take for your son.
These verses, though, speak only about marrying people from the Canaanite nations, and do not explicitly address marrying other Gentiles.1 As such, it is unclear how to view Esther's marriage to Achashverosh. Was it prohibited by the Torah or only by the later Rabbinic enactments?2 If the latter, was this prohibition already in place at the time of Mordechai and Esther?
Furthermore, even if one posits that it is a Torah level prohibition, it is not at all certain whether relations with an idolater3 are included among the illicit relations for which one is obligated to forfeit one's life.4 On the other hand, according to the Bavli Sanhedrin, a public transgression (and Esther's marriage was certainly publicly known) can turn even a minor crime into a desecration of God's name for which one must suffer martyrdom.5 Thus, there is certainly room to wonder about how the halakhah might have ruled or been applied in the time of Esther.