1) WHICH KOHEN PERFORMS "NESI'AS KAPAYIM"?
QUESTION: The Mishnah states that the person who normally reads the Haftarah is entitled to perform Nesi'as Kapayim (if he is a Kohen).
What does the Mishnah mean? All of the Kohanim present are required to recite Birkas Kohanim together! Why does the Mishnah say that only the Kohen who reads the Haftarah is entitled to perform Nesi'as Kapayim? (TOSFOS YOM TOV)
ANSWERS:
(a) The TOSFOS YOM TOV answers that the Mishnah indeed does not need to say that this particular Kohen performs Nesi'as Kapayim, as all of the Kohanim perform Nesi'as Kapayim together. The Mishnah says these words only because of the statement at the end of the Mishnah, which says that a minor may not perform Nesi'as Kapayim. To maintain its style, the Mishnah mentions here that the one who reads the Haftarah also performs Nesi'as Kapayim.
(b) The TOSFOS YOM TOV answers further that perhaps the Mishnah means that this Kohen is the one who starts Birkas Kohanim before the other Kohanim. Starting Birkas Kohanim was an honor reserved for the most venerable Kohen.
The TUREI EVEN, however, rejects this answer on the grounds that there is no source in the Gemara that the act of starting Birkas Kohanim was a form of honor for a Kohen.
(c) The TUREI EVEN answers based on the Gemara in Sotah (31a). The Gemara there teaches that when all of the worshippers in the synagogue are Kohanim, all except for ten go up to perform Nesi'as Kapayim. The Mishnah here teaches that in such a case (when only some of the Kohanim perform Nesi'as Kapayim) the one who reads the Haftarah is honored with being one of the Kohanim who performs Nesi'as Kapayim.
(d) The RASHASH suggests that the Mishnah refers to a case in which the Kohen serves as the Shali'ach Tzibur. The Mishnah teaches that even though he is the Shali'ach Tzibur, he also performs Nesi'as Kapayim.
The Mishnah in Berachos (34a) states that when the Shali'ach Tzibur is the only Kohen in the synagogue, he should not perform Nesi'as Kapayim because he might become confused and forget which words he last recited in the repetition of the Shemoneh Esreh. However, if he feels confident that he will not become confused after he recites Birkas Kohanim and he will return to the words of the repetition of the Shemoneh Esreh, he is permitted to perform Nesi'as Kapayim. The Poskim rule that when other Kohanim are present, the Shali'ach Tzibur should let them perform Nesi'as Kapayim and he should not join them, even if he is certain that he can return to his recitation of the Shemoneh Esreh without becoming confused. (See HAGAHOS MAIMONIYOS, end of Hilchos Nesi'as Kapayim.)
The Rashash suggests that the Mishnah here means that even though this Kohen is the Shali'ach Tzibur and there are other Kohanim present, he may perform Nesi'as Kapayim because he read the Haftarah. He should not lose the privilege of Nesi'as Kapayim as a result of serving as the Shali'ach Tzibur.
2) HALACHAH: AT WHAT AGE MAY A KOHEN PERFORM "NESI'AS KAPAYIM"?
QUESTION: The Mishnah states that a Katan (a minor under the age of Bar Mitzvah) may not perform Nesi'as Kapayim. The Mishnah implies that one who is no longer a Katan (he has reached the age of Bar Mitzvah or has physical signs of maturity) may perform Nesi'as Kapayim.
TOSFOS (DH v'Ein) asks that the Mishnah contradicts the Gemara in Chulin (24b) which says that "when a man's beard becomes full, he may perform Nesi'as Kapayim." The Gemara there implies that it is not enough for a young man to have the basic signs of maturity.
Both the Mishnah here and the Gemara in Chulin contradict the Gemara in Sukah (42a) which implies that even a minor may perform Nesi'as Kapayim.
How are these three sources to be reconciled?
ANSWER: TOSFOS suggests that the three apparently contradictory sources refer to three separate age groups.
(a) A minor may perform Nesi'as Kapayim only together with adult Kohanim (for the sake of Chinuch; see Shulchan Aruch OC 128:34). He may not perform Nesi'as Kapayim when he is the only Kohen present.
(b) A young man who is no longer a minor but who does not have a full beard may perform Nesi'as Kapayim by himself occasionally but not on a regular basis. The reason why he may perform Nesi'as Kapayim occasionally is in order for others to know that he is a Kohen.
TOSFOS in Sukah (42a-b, DH ha'Yode'a) adds that on days designated for prayer, such as Yom Kippur, a Kohen whose beard is not full should not perform Nesi'as Kapayim.
(c) When a Kohen's beard is full he may perform Nesi'as Kapayim on a regular basis even by himself.
HALACHAH: The SHULCHAN ARUCH (OC 128:34) distinguishes between the three different age groups as Tosfos categorizes them. However, the Shulchan Aruch does not cite Tosfos' ruling in Sukah that a Kohen whose beard has not filled out should not perform Nesi'as Kapayim on days of prayer like Yom Kippur. The BI'UR HALACHAH (DH v'Lo) wonders why the Poskim omit this ruling.
(The Poskim write that the Halachic requirement that a Kohen have a full beard applies only to a man who is under the age of eighteen, or a man who is over the age of eighteen and has no facial hair growth at all. One who is over the age of eighteen and has a small beard is classified as a person whose beard has filled out; see Shulchan Aruch ibid. and Mishnah Berurah OC 128:126.)
The YESHU'OS YAKOV maintains that the custom of Ashkenazim is that a minor does not perform Nesi'as Kapayim at all. This is based on the opinion of RASHI in Sukah (42a) who seems to disagree with Tosfos' ruling that permits a minor to recite Birkas Kohanim together with adult Kohanim. Nevertheless, in many places of worship in Eretz Yisrael (such as in the Beis Midrash of HAGA'ON RAV YISRAEL ZEV GUSTMAN zt'l) it is the custom for minors to recite Birkas Kohanim together with adult Kohanim. (M. Kornfeld) (See Insights to Chulin 24:5.)