1) HALACHAH: RECITING A BLESSING BEFORE BIRKAS KOHANIM
QUESTION: When the students of Rebbi Elazar ben Shamua asked him how he merited to live a long life, he answered that he was always careful not to walk through a synagogue to use it as a shortcut, he was careful not to walk among the students when they were already seated on the ground in the study hall (lest he appear as though he was trampling upon their heads), and he never performed Birkas Kohanim without reciting a blessing beforehand. The Gemara explains that the blessing he recited before Birkas Kohanim was, "Baruch... Asher Kideshanu bi'Kedushaso Shel Aharon v'Tzivanu l'Varech Es Amo Yisrael b'Ahavah."
Why did Rebbi Elazar ben Shamua claim to have a special merit for reciting a blessing over the performance of the Mitzvah of Birkas Kohanim? A blessing is recited prior to the performance of every Mitzvah!
(a) The ME'IRI here writes that the blessing for the Mitzvah of Birkas Kohanim is merely a "Hidur Mitzvah" and does not prevent the Mitzvah from being performed (it is not "Me'akev"). Accordingly, Rebbi Elazar ben Shamua was crediting himself for being careful with this Hidur. (See also BI'UR HA'GRA to OC 128:13.)
(b) The Me'iri in Megilah, however, explains that Rebbi Elazar ben Shamua was not referring to the blessing for the Mitzvah of Birkas Kohanim, but to the prayers of "Yehi Ratzon" and "Ribon ha'Olamim." By being careful to recite these prayers every time he recited Birkas Kohanim, "he showed his intense love and affection for the people."
(c) The RADAL writes that in earlier generations it was not the practice to recite a blessing (Birkas ha'Mitzvos) for Birkas Kohanim. They reasoned that since Birkas Kohanim itself is a blessing, it is inappropriate to recite a blessing over the recitation of another blessing. Similarly, no blessing was instituted for the recitation of the blessing of Birkas ha'Mazon or the blessing of Kidush (according to the opinion that it is mid'Oraisa), and no blessing was instituted for the recitation of any Birkas ha'Shevach or Birkas Hoda'ah.
The TUREI EVEN in Megilah adds that perhaps it was Rebbi Elazar ben Shamua himself who instituted the blessing of Birkas Kohanim, and until his time they did not recite a blessing for that Mitzvah, just as there are a number of other Mitzvos for which no blessing is recited.
The NETZIV (in EMEK SHE'EILAH 125) disagrees with the Turei Even. He argues that there certainly is an obligation to recite a blessing over the performance of every Mitzvah. Although there are some Mitzvos for which no blessing is recited, the Rishonim give specific reasons for why no blessing was instituted for those Mitzvos. None of those reasons apply to Birkas Kohanim. Nevertheless, the Netziv finds support for the Turei Even from the words of the BA'AL HA'ME'OR (end of Rosh Hashanah, DH u'Mah she'Nahagu). The Netziv explains that when a Mitzvah comes in the context of other blessings (such as Keri'as Shema during Shacharis and Ma'ariv), the Rabanan did not establish a separate blessing for the Mitzvah. (This is why there is no blessing of "Asher Kideshanu... Al Ker'ias Shema" for the Mitzvah d'Oraisa of reciting the Shema, and why there is no blessing of "Al Birkas ha'Mazon" for the Mitzvah d'Oraisa of reciting Birkas ha'Mazon.) Since Birkas Kohanim is recited immediately following the blessing of "ha'Tov Shimcha u'Lecha Na'eh l'Hodos," it does not need its own blessing. (See Netziv there for a lengthy explanation of the Gemara here, according to both the Ba'al ha'Me'or and the Ramban at the end of Rosh Hashanah.)
(d) RAV MOSHE FEINSTEIN zt'l (IGROS MOSHE OC 4:21:2) explains that Rebbi Elazar ben Shamua would recite the blessing before Birkas Kohanim even when he served as Shali'ach Tzibur. The Mishnah in Berachos (34a) states that a Shali'ach Tzibur who is a Kohen should not recite Birkas Kohanim at all unless he is confident that he will be able to continue the recitation of Shemoneh Esreh without becoming confused. Rebbi Elazar ben Shamua was confident that he would not become confused and he recited Birkas Kohanim as well as the blessing before it. Since the Halachah was established according to his practice, in the merit of the additional blessing recited by the Shali'ach Tzibur he merited a long life. (Y. SHAW)
2) HALACHAH: WHO CALLS OUT "KOHANIM" FOR BIRKAS KOHANIM
QUESTION: The Gemara teaches that the "Korei," the one who calls "Kohanim," may not call up the Kohanim until the Tzibur finishes saying "Amen" to the previous blessing. The Sifri (Parshas Naso) and the Yerushalmi (cited by Tosfos to 38a, DH l'Shnayim) explain that the "Korei" who calls up the Kohanim is the "Chazan."
Who is the "Korei" or "Chazan" who calls up the Kohanim to recite Birkas Kohanim?
(a) RASHI here (and end of 38a) explains that it is the Shali'ach Tzibur who calls up the Kohanim. This is also the ruling of the RAMBAM (Hilchos Tefilah 14:8).
(b) However, RABEINU TAM (cited by Tosfos to Berachos 34a, DH Lo Ya'aneh, and by the Tosfos ha'Rosh here) rules that it would be an interruption in the Shemoneh Esreh if the Shali'ach Tzibur would call up the Kohanim to Birkas Kohanim. Therefore, someone else should call "Kohanim."
Rabeinu Tam finds support for his explanation from the wording of the Gemara, which says that the "Korei" calls out "Kohanim," and the "Shali'ach Tzibur" recites "Sim Shalom," implying that they are two different people.
Rabeinu Tam explains that when the Sifri says that the "Chazan" calls out "Kohanim," the word "Chazan" does not refer to the Shali'ach Tzibur but rather to the "Chazan ha'Keneses" (the "Shamash," or the one who takes care of synagogue matters; see Mishnah, 40b). Rashi apparently distinguishes between the "Chazan ha'Keneses," a term which does not refer to the Shali'ach Tzibur (Rashi to Ta'anis, beginning of 15b) and "Chazan," a term which does refer to the Shali'ach Tzibur (as the Aruch writes in Erech "Chazan," and as is evident from Rashi to Ta'anis 16b, DH Zeh ha'Ma'amid Chazan).
The ROSH (Megilah 3:21) rules like Rabeinu Tam.
(c) RABEINU YEHUDAH HE'CHASID (Berachos 34a) suggests a compromise. When no Kohanim are present, the common practice is for the Shali'ach Tzibur to say, "Elokeinu... Barcheinu va'Berachah ha'Meshuleshes...." The reason why the Shali'ach Tzibur may say that prayer and it is not considered an interruption in his Shemoneh Esreh is that it is a Tefilah (prayer) and not just a "Keri'ah" (announcement). Hence, even when there are Kohanim present, the Shali'ach Tzibur may say "Elokeinu..." quietly as a Tefilah, and when he gets to the word "Kohanim" he says it out loud in order to call up the Kohanim. It is not considered an interruption because it is part of the Tefilah.
This was the practice of the MAHARAM MI'ROTENBURG as cited by the Hagahos Maimoniyos (Hilchos Tefilah 14:7).
HALACHAH: The BEIS YOSEF cites sources which say that the Maharam retracted his view and ruled that the Shali'ach Tzibur should not recite "Elokeinu..." when Kohanim are present. The only reason why the Shali'ach Tzibur recites it when no Kohanim are present is as a substitute for the "Yehi Ratzon" prayer which the Kohanim ordinarily recite before Birkas Kohanim. When Kohanim are present, the Kohanim themselves recite the prayer of "Yehi Ratzon" and thus there is no point for the Shali'ach Tzibur to say it as well. Therefore, the SHULCHAN ARUCH (OC 127:10) rules like the Rambam, that the Shali'ach Tzibur calls out "Kohanim."
The REMA, however, mentions the custom for the Shali'ach Tzibur to say "Elokeinu" quietly until the word "Kohanim" and to say "Kohanim" out loud. The VILNA GA'ON, however, followed the opinion of Rabeinu Tam, that someone else should call up the Kohanim and not the Shali'ach Tzibur (Ma'aseh Rav #168). Many Ashkenazic communities in Eretz Yisrael follow the practice of the Vilna Ga'on.
3) WHEN MAY THE KOHANIM TURN AROUND
QUESTION: The Gemara teaches that the Kohanim may not turn around after they have concluded the recitation of Birkas Kohanim until the Shali'ach Tzibur begins the blessing of "Sim Shalom."
RASHI (DH la'Akor) presents the procedure of Birkas Kohanim. He writes that as soon as the Tzibur finishes answering "Amen" to the last blessing of Birkas Kohanim, the Kohanim may turn around, and then the Shali'ach Tzibur begins "Sim Shalom."
Rashi seems to contradict the Gemara. He writes that the Kohanim may turn around before the Shali'ach Tzibur begins "Sim Shalom," but the Gemara clearly says that they must wait for the Shali'ach Tzibur to begin "Sim Shalom" before they turn around.
ANSWER: The MAHARSHAL writes that according to Rashi, the Gemara means that the Kohanim turn around at the time the Shali'ach Tzibur normally begins "Sim Shalom," which is after the last person in the Tzibur finishes saying "Amen."
How does Rashi know to explain the Gemara in this manner and not in its literal sense?
The DEVAR AVRAHAM (1:31:5) quotes a colleague who found a source for Rashi's words. The SHE'ILTOS (#125) clearly writes that the Kohanim may not turn around until the last person in the Tzibur answers "Amen." Rashi's text of the Gemara here may have had that Girsa, or he understands the Gemara here (as the Maharshal explains) based on what the She'iltos writes. The view of the She'iltos seems to be a more logical practice, since -- after the last "Amen" is finished -- the blessing of Birkas Kohanim is completed and there is no reason for the Kohanim to have to wait for the Shali'ach Tzibur to begin "Sim Shalom" before they turn around.