We learned in the Mishna on yesterday’s daf that if a man married to two women who share the same name tells a scribe to write a geṭ for one of them and that he will decide later on which wife to divorce, the geṭ would be invalid. From this ruling our Gemara wants to conclude that en berera – that we do not take seriously a later action which clarifies an earlier issue. The question of whether or not halakha recognizes berera – the later clarification – is a topic discussed in relation to many laws throughout the Talmud. In an apparent contradiction to the conclusion of our Mishna, the Gemara brings a rule about the korban Pesaḥ, in which it appears that yesh berera – that a later action can clarify an earlier halakhic situation.
The Mishna (Massekhet Pesaḥim 89a) teaches that when a father tells his children, “I will slaughter the korban Pesaḥ on behalf of whoever gets to Jerusalem first,” whichever child reaches first is credited with the sacrifice for himself, and his siblings are included as well. This is the case even though the rule is that the only people who participate in a korban Pesaḥ are those who had arranged to do so in advance, apparently supporting the idea that yesh berera.
In response to this question, Rav Yehuda points out that the case of korban Pesaḥ cannot be compared to giṭṭin, since Rabbi Yohanan explains that the children under discussion are adult children who are obligated in the sacrifice. According to this approach, the father would certainly have needed to include his children in the sacrifice before it was slaughtered, and that he, in fact, did so. The father did not disclose this to his children however, and in the interest of encouraging their enthusiasm, made them think that only the child who arrived in Jerusalem first would merit participation in the korban.