This halakha was also taught in the previous mishna (26a), and it is cited in this mishna according to the opinion of Rabbi Shimon. The Gemara asks: But didn’t Rabbi Shimon say: Two sisters neither perform ḥalitza nor enter into levirate marriage? Because these women are eligible for levirate marriage according to Torah law, they are considered the sisters of a woman with whom he has a levirate bond. In this case, Rabbi Shimon exempts them from both ḥalitza and levirate marriage. Why, then, does the mishna require them to perform ḥalitza?

The Gemara answers: It is a rabbinic decree due to the general case of a prohibition resulting from a mitzva. If they did not perform ḥalitza in this case, where they are sisters, there is a concern that people would assume that their exemption from ḥalitza stemmed not from their status as sisters but rather due to the prohibition. This would lead to the mistaken conclusion that women who are forbidden due to a mitzva do not require ḥalitza. Therefore, the Sages issued a rabbinic decree requiring ḥalitza in this case.

The Gemara asks: This works out well for her, as she is forbidden due to the prohibition resulting from a mitzva. It is appropriate to require ḥalitza with her, to demonstrate that ḥalitza is generally applied in cases where there is a prohibition resulting from a mitzva. But with regard to her sister, what is there to say? Why must she perform ḥalitza as well? The Gemara answers: There is a rabbinic decree with regard to her sister due to her.

The Gemara asks: If Rabbi Shimon issues a decree in this case requiring ḥalitza for the sister, out of concern for confusion, then there is a difficulty: But, with regard to a forbidden relative we do not issue a decree requiring ḥalitza due to her sister; why does Rabbi Shimon issue a rabbinic decree requiring ḥalitza with a woman forbidden due to a prohibition resulting from a mitzva and not with a woman who is a forbidden relative? The Gemara answers: Forbidden relatives are different, as people learn the halakhot pertaining to them because they are stated explicitly in the Torah and are well known to all, and the ruling has publicity. Therefore, there is no concern lest people mistakenly confuse this case with cases of yevamot who are not sisters. Prohibitions resulting from mitzvot are not, however, explicit in the Torah, nor are they generally known.

MISHNA: In the case of three brothers, two of whom were married to two sisters, and one who was single, the following occurred: The husband of one of the sisters died childless, leaving behind his wife, and the single brother performed levirate betrothal [ma’amar] to this wife. The single brother performed an act of betrothal to the yevama but did not yet consummate the marriage by engaging in sexual intercourse. Afterward, the second brother died, and therefore the second brother’s wife, the sister of the betrothed, happened before the single brother for levirate marriage as well.

In this case, Beit Shammai say: His wife remains with him. The woman he betrothed is considered like his wife, and he is not required to divorce her. And this other woman leaves the yavam and is exempt from levirate marriage as the sister of a wife. Beit Hillel say: Being as he had not yet entered into marriage with the first woman, he is required to perform levirate marriage with both women. Therefore, he divorces his wife, i.e., the woman to whom he performed levirate betrothal, with a bill of divorce, which nullifies levirate betrothal, and by ḥalitza, which nullifies the levirate bond. And, he sends away the wife of his second brother with ḥalitza as well. They comment: This is the case that was referred to when the Sages said: Woe unto him for his wife and woe unto him for the wife of his brother. Due to the combination of circumstances, he loses them both.

GEMARA: The Gemara asks: What does the mishna’s formulation of the term: This is, which indicates limitation and exactitude, come to exclude? The Gemara answers: It excludes that statement of Rabbi Yehoshua (109a). There, Rabbi Yehoshua holds that if a man is married to a minor when her sister happens before him for levirate marriage, he must send both of the women away. He said there: Woe unto him for his wife and woe unto him for the wife of his brother. From the language in the mishna here, we learn that we do not act in accordance with his opinion. Rather, we act either in accordance with the opinion of Rabban Gamliel or in accordance with the opinion of Rabbi Elazar. According to the opinion of both of these tanna’im in the mishna (109a), despite the conflict between the brother’s marriage to the minor and the levirate bond with her sister, there is still a way for him to marry one of the women.

§ With regard to the main issue of levirate betrothal, it would seem from this mishna that Beit Shammai hold that levirate betrothal has the legal force of levirate marriage. However, Rabbi Elazar said: Do not say that levirate betrothal acquires the woman as a full-fledged acquisition according to the opinion of Beit Shammai, such that the first woman becomes his wife to the extent that if he wants to divorce her a bill of divorce would suffice without an act of ḥalitza. Rather, for Beit Shammai, levirate betrothal acquires the woman only insofar as it precludes a rival wife from entering levirate marriage. The legal force of levirate betrothal is limited to preventing the rival wife of the sister from performing levirate marriage; she is exempt from both levirate marriage and ḥalitza.

Rabbi Avin said: We, too, learn in the mishna a proof that levirate betrothal is not a full-fledged act of acquisition, even according to Beit Shammai. The mishna at the beginning of this chapter (26a) teaches that when two sisters who are yevamot happen before two brothers for levirate marriage, if the brothers married their wives before consulting the court, then Beit Shammai say: They may maintain them as their wives. From here it can be deduced: If they already married them, yes, they may maintain them. However, marrying them ab initio, no, this is prohibited due to the prohibition against marrying the sister of a woman with whom one has a levirate bond.