Decree of Rabba: Shofar on Rosh Hashanah on Shabbath
The lecture is about Rosh Hashanah which falls out on Shabbath. We refer to Rosh Hashanah 4:1 18b in Vilna edition. There we find the Gemara discussing why we do not blow the shofar outside of the Beth Hamikdash. The Yerushalmi cites a verse (which the Bavli does also): One verse says: The day on which you blow a teru’ah. Another verse says: “a day in which you commemorate the blowing of the shofar. How do you reconcile the verses? Is it the actual blowing or a commemoration of the blowing? The Gemara says: If this happens on a weekday then you do blow the shofar on Rosh Hashanah but if Rosh Hashanah falls out on Shabbos we recall it but we do not blow the shofar. The Bavli goes on to reject this reason. The truth is that it is a little difficult to sustain this reason and the concept of blowing shofar in beth din after the destruction of the Beth Hamikdash.
The Bavli comes to the famous decree of Rabba which applies to Shofar, Lulav, Megillah that we do not use them on Shabbath lest you come to take it out to a public thoroughfair a distance of four cubits in order to learn how to blow. However, the Yerushalmi does not know about the Gezerah of Rabba. Rabba’s Gezerah came after the time of the Yerushalmi and it therefore remains with the derivation from the verses and therefore is compelled to say that sometimes we blow and sometimes we do not blow.
The Yerushalmi in Sukkah says something similar about Lulav and Ethrog but there the Gemara concludes that the reason we do not take them on Shabbath is because of the Gezerah of Rabba