Birchat Kohanim: Davar Shebikedusha or Din of Tzibur in Rambam and Yerushalmi

The shiur opens by reviewing two previously established principles: (1) According to the Rambam (רמב"ם), the Kaddish before Yishtabach in the morning is required because Kriyat Shema is an avodah, and avodah requires a davar shebikedusha (i.e., Kaddish). Additionally, a minyan is needed for kabbalat ol malchut shamayim b'rabim—one person accepting God's kingship makes God a rebbe, but ten people make Him a king. By Maariv, however, there is no din of semikhut geulah l'tefillah as an avodah, so no Kaddish is required before Borchu. (2) The Rambam explicitly states that in Shacharit one must say Shemoneh Esrei "miyad" (immediately) after Ga'al Yisrael, but by Maariv no such immediacy is required. This demonstrates that the din of semikhut geulah l'tefillah in Shacharit is part of the avodah itself—like knocking on the king's door and entering immediately—whereas by Maariv it is not. The shiur then clarifies that according to the Rambam, chazarat hashatz is not a davar shebikedusha but rather a din of tefillah b'tzibur. The kedusha recited during chazarat hashatz is not a separate davar shebikedusha; it is merely the nusach (text) of the third bracha, as seen explicitly in the Rambam's Seder HaTefillah where he describes it as part of the bracha and not as an independent kedusha. This is important because if chazarat hashatz were a davar shebikedusha, one could recite Kaddish afterward even if part of the minyan left; but since it is only a tzibur din, the Mechaber rules that Kaddish cannot be said if the minyan is lost. The Rama disagrees and permits Kaddish because he considers chazarat hashatz a davar shebikedusha.