Moed Katan 18 - 24
This issue was sponsored in merit for the complete recovery of Moshe Zalman ben Rivka
Even on Tisha B'Av!
Even though weddings cannot take place during Chol Hamo'ed (the intermediate days of a Festival), it is permitted to make airusin (the formal union of man and woman which forbids her to anyone else, and requires a divorce to dissolve this union, but does not allow the pair to live together until the nissuin at the time of the chupah). The Sage Shmuel explained that the reason the Sages permitted this transaction to take place despite their ban on other transactions is that there is an urgency involved - someone else may marry the woman before he does.
But how could Shmuel advocate such a concern, asks the gemara, when he is the author of the statement that each day a Heavenly voice announces which woman will be married to which man?
The answer given is that Shmuel's concern was not over a competitor beating him out by natural means, but rather that the competitor might invoke the power of prayer to win this woman.
An illustration of such a threat is provided in an incident in which the Sage Rava overheard a man praying that he win the hand of a particular woman. Rava reprimanded him for such prayer, because if she was destined for him there was no need for prayer; and if she was destined for another, then his unfulfilled prayer would lead him to a loss of faith. Rava subsequently overheard this same fellow, already resigned to the possibility that the woman he sought might not be destined for him, pray that if she indeed would not be his, that either she die before marrying another or that he himself die before she gets married. Rava reprimanded him for this prayer as well. This incident serves as evidence that there is danger that a competitor's prayer can cause a man to lose his intended and destined mate. Making airusin on Chol Hamo'ed, therefore, becomes an urgency to assure that she will not become the victim of such a prayer.
This is the explanation of the gemara offered by Rashi, and it seems to revolve around the assumption that prayer cannot win a woman for a man for whom she was not predestined, but can prevent her marriage to another. Maharsha already points out that this runs counter to the literal understanding of Shmuel's words which indicate that prayer can result even in a competitor actually gaining the woman not predestined for him.
Ritva has another approach. Prayer, he contends, has the power to change what has been predestined, and this is why the Sages allowed airusin even on Chol Hamo'ed. Why then did Rava reprimand the fellow who was simply trying to use the power of prayer? Because Rava's wisdom told him that this woman was not really suited for the praying fellow, and that he would eventually regret marrying her. This is why he told him in his second reprimand not to pray for this woman because it is not for his benefit.
Learning From the Forefathers
Can we learn a halacha from an event in the Torah which took place before the Torah was given? We seem to get conflicting signals on this issue from statements in the Jerusalem Talmud which Tosefot cites in our mesechta. Regarding the source for a seven-day period of mourning, our gemara cites a passage in the prophecy of Amos (8:10) equating festival with mourning. Why, asks Tosefot, don't we learn this from the seven-day period of mourning which Yosef observed for his father (Bereishet 50:10). The Jerusalem Talmud's explanation, answers Tosefot, is that we don't learn laws from what took place before the Torah was given.
Yet, regarding a previous gemara (Mo'ed Katan 8b) which bans getting married during the intermediate days of a Festival, as it is wrong to mix one simcha with another, Tosefot cites the Jerusalem Talmud offering as a source the incident with Yaakov and Lavan: Lavan insisted that Yaakov complete the seven days of celebration with Leah before being allowed to marry Rachel (Bereishet 29:27).
Rabbi Zvi Hirsh Chayot, in his commentary printed at the back of the Vilna Shas, calls attention to this contradiction regarding learning from events that happened before the Torah was given. He refers us to his "Torat Hanevi'im" in which he discusses this issue at length. In his comprehensive review of all the rules we do or do not learn from pre-Torah days, his basic point is that only when there is something which logic dictates as proper behavior do we cite a source from pre-Torah times as scriptural support for doing so. Not mixing simchas, so that proper focus can be given to each, is a logical point, as Tosefot himself notes, so we can rely on the example of Lavan and Yaakov as support. The length of time for mourning, however, is more a matter of law than logic, and can therefore not be deduced from what Yosef did for his father in pre-Torah times.