Study Yevamot folio 28B with parallel Hebrew-English text, traditional commentary, and modern study tools. Free access to Babylonian Talmud online.
Text Excerpt
איסור מצוה ואיסור קדושה — חולצת ולא מתייבמת! התם, איסור מצוה לחודה, הכא, איסור מצוה, ואחותה.
If a prohibition resulting from a mitzva or a prohibition stemming from sanctity will be transgressed through the levirate marriage, then the woman must perform ḥalitza and she may not enter into levirate marriage. The Talmud answers: There is a novelty here: There, where the halakha is reviewed in general terms, it speaks of a prohibition due to a mitzva alone. One woman happened before the yavam for levirate marriage and it is only as a result of this prohibition that she is prevented from entering levirate marriage. Here, there is a prohibition resulting from a mitzva and, in addition, her sister happened before the yevamin for levirate marriage together with her.
סלקא דעתך אמינא: ליקום איסור מצוה במקום איסור ערוה — ותתייבם, קא משמע לן.
It might enter your mind to say: Let the prohibition resulting from a mitzva stand in the same place, i.e., level of severity, as the prohibition against forbidden relatives. Consequently, the woman who is forbidden to the yavam is considered a forbidden relative and her sister is permitted to him. Despite the fact that the prohibition resulting from a mitzva is not as severe, here it is given equal status, and we might say: Let her sister enter into levirate marriage. Therefore, this comes to teach us that this is not the case.
The Talmud asks: And why in fact does her sister not enter into levirate marriage? The Talmud answers: Her sister is forbidden to him because by Torah law the prohibited woman is still set before the yavam for levirate marriage. Were he to take the sister in levirate marriage he would essentially be encountering the sister of the woman with whom he has a levirate bond. It might enter your mind to say that due to the mitzva of levirate marriage, the rabbis did as they did and nullified their decree prohibiting the sister of a woman with whom the yavam has a levirate bond from entering levirate marriage, when the original sister is forbidden only as the result of a mitzva. Therefore, it teaches us that they did not cancel their decree in this situation.