- איסור מצוה ואיסור קדושה
The next Mishnah states: איסור מצוה ואיסור קדושה חולצת ולא מתייבמת – an issur mitzvah and an issur kedushah do chalitzah but not yibum and defined an issur mitzvah as שניות מדברי סופרים – secondary arayos who are prohibited by the Rabbanon, and an issur kedushah as an almanah to a Kohen Gadol, a gerushah or a chalutzah to a Kohen, a mamzeres or nesinah to a Yisroel, or a bas Yisroel to a nasin or a mamzer. The Gemara asks why the Tanna uses the term issur mitzvah, and Abaye answers: מצוה לשמוע דברי חכמים – it is a mitzvah to listen to the words of the Chochomim. It then asks why the Tanna used the term issur kedushah, and answers because the passuk states regarding Kohanim: קדשים יהיו לאלקיהם – They shall be sanctified to their G-d, and this refers to a Kohen marrying certain women. A Baraisa is brought that taught that Rebbe Yehudah switched the definitions, and the Gemara explains the reason that an almanah to a Kohen Gadol, and gerushah and chalutzah to a regular Kohen, are called issur mitzvah, is because it is written regarding the prohibitions of Kohanim, "אלא המצות" – these are the mitzvos. Rava explains that שניות are called issur kedushah because of the principle of קדש עצמך במותר לך – sanctify yourself by refraining from what it permitted to you.
- Rav’s answer as to why an almanah from erusin is forbidden to do yibum to a Kohen Gadol
The Gemara notes that the Mishnah stated that an almanah may not be taken in yibum by a Kohen Gadol, implying that it makes no difference if she fell to yibum from nisuin, or erusin. It asks that while it is understandable that she is forbidden if she falls from nisuin, because she is prohibited by the mitzvas aseh that a Kohen must marry a virgin, and the lo sa’aseh that he may not take a widow, ואין עשה דוחה לא תעשה ועשה. But in the case of the almanah falling from erusin, לא תעשה גרידא הוא – it is only a lo sa’aseh that forbids her to him. Rashi explains that since she is a virgin, she only has the lo sa’aseh of a Kohen being forbidden to an almanah. Therefore, יבא עשה וידחה לא תעשה – let the aseh of yibum, override the lo sa’aseh against a Kohen Gadol marrying a widow? Rav Gidel said in the name of Rav: The passuk states: "ועלתה יבמתו השערה" – then his yevamah shall go up to the gate for chalitzah. Since it was unnecessary to state “his yevamah” since the passuk already referred to her as that, it is coming to teach, יש לך יבמה אחת שעולה לחליצה ואינה עולה ליבום – there is a yevamah who is subject to chalitzah and not to yibum. And who is this? חייבי לאוין – It is one who is prohibited to the yavam by a lav. Rav’s answer will be analyzed and ultimately come to be refuted.
- גזירה ביאה ראשונה אטו ביאה שניה
After Rav’s answer is refuted, Rava attempts a number of times to resolve the question as to why the almanah from erusin is prohibited from yibum to a Kohen Gadol, given that she is only prohibited by one lav. He then concludes that the reason she is forbidden is that it is a גזירה ביאה ראשונה אטו ביאה שניה – a gezeirah that the yavam not do the first act of relations for the mitzvah of yibum, out of concern that he might have a second act of relations, which is not a fulfillment of a mitzvah. Mid’Oraysa, the yavam is permitted to her for the first act of relations, as it is the mitzvah of yibum, but then must divorce her immediately afterward because he will not be doing a mitzvah anymore when having a second act of relations, and there is still a lav. The Rabbanon were concerned that he would not divorce her promptly, and therefore decreed that she do chalitzah, not yibum. Rava attempts to retract this answer, but his retraction will be refuted.