With regard to the mitzva of aravah that was discussed on yesterday’s daf, Rabbi Abbahu quotes Rabbi Yohanan as saying that it was a mitzva established by the prophets (yesod nevi’im), while Rabbi Yehoshua ben Levi taught that it was a tradition of the prophets (minhag nevi’im). The difference between the two opinions is that if the aravah is a yesod nevi’im, the implication is that the prophets established it as an obligation, and someone who fulfills the commandment will make a berakhah on it beforehand. If, on the other hand, it is a minhag nevi’im, that merely indicates that the prophets themselves performed this ritual and that others, seeing them do it, chose to accept it upon themselves. If that is the case, the aravah does not merit a berakhah like other Rabbinic commandments.
Rabbi Zeira said to Rabbi Abbahu: Did Rabbi Yohanan actually say that? Didn’t Rabbi Yohanan say in the name of Rabbi Nehunya of the valley of Beit Hortan: The halakha of the ten saplings, the mitzvah of the willow branch in the Temple, and the mitzva of the water libation on the altar during the festival of Sukkot are each a halakha transmitted to Moses from Sinai? How then could he attribute the origin of the mitzva of the willow branch to the prophets?
After a moment’s hesitation, Rabbi Abbahu explained that this commandment is, in fact, a halakhah leMoshe mi-Sinai, however the tradition was forgotten and the prophets came and reestablished it.
The commentaries raise a basic question about this answer. In general we believe that nevi’im do not have the ability to give new rulings about matters of halakhah through their powers of prophecy (according to the Rambam attempting to do so is an indication of a false prophet). According to that, how could the nevi’im reestablish a forgotten halakha leMoshe mi-Sinai? In his commentary to Massekhet Sukka, Rav Zvi Hirsch Chajes suggests that these prophets did not reestablish the mitzva of aravah based on their prophecy, rather they did so based on their ability to analyze and study the relevant texts and halakhot.