6.Washing Hands Before the Blessing
Before the Kohanim raise their hands to bless the nation, they must wash their hands up to their wrists. There is an allusion to this in the verse (Psalms 134:2), "Lift up your hands in holiness and bless Hashem." Any Kohen who did not wash his hands may not bless the people (Sotah 39a). Eminent Rishonim disagree regarding the reason for this hand washing. According to the Rambam (Tefillah 15:5), the obligation to wash one’s hands only exists when they are dirty. Therefore, a Kohen who washes his hands in the morning and is careful not to touch dirty parts of his body is not obligated to wash his hands again before Birkat Kohanim. However, according to Rashi and Tosafot (Sotah 39a), even clean hands must be washed and sanctified in honor of Birkat Kohanim.
In practice, we are stringent, and a Kohen whose hands are clean must also wash them before Birkat Kohanim, like the opinion of Rashi and Tosafot. However, no berachah is recited on the washing even if he touched dirty places before washing, since there is doubt whether or not the Chachamim instituted a berachah for it (Mishnah Berurah 128:24, based on the Eliyah Rabbah).
It seems from the Zohar that this washing was intended to sanctify the Kohanim, and their hands, in preparation for the berachah. In order to increase the level of sanctity, it is customary that a Levi pour the water on the hands of the Kohanim. When there is no Levi present in the synagogue, it is advisable that a firstborn, who possesses some amount of sanctity, wash the hands of the Kohanim. In the absence of a Levi and a firstborn, the Kohen washes his own hands (Shulchan Aruch 128:6; Mishnah Berurah 22).
When the Kohen is concerned that perhaps there will not be water in the synagogue with which to wash his hands before blessing the people, he washes them in his house before the prayer service and takes care to keep them clean. In that way he can recite the blessing upon the people. However, if the Kohen is not careful to keep his hands clean after the morning washing, and he does not have water to wash them before Birkat Kohanim, he may not ascend the duchan to bless the nation.
In every situation where the Kohen is forbidden to bless the people, it is advisable that he leave the synagogue before the time of Birkat Kohanim, so that the gabbai will not mistakenly call him up to ascend the duchan when he is not permitted to do so. If the Kohen remains present and he is not called, there is concern that perhaps people will think that he is an invalid Kohen.
7.Yisrael’s Participation in Birkat Kohanim
When the time arrives to recite Birkat Kohanim, the Kohanim are not permitted to start the berachah until the chazan or the gabbai announces "Kohanim." This is because the Torah states (Numbers 6:23), "Say to them," denoting that Moshe, who is not a Kohen, must tell the Kohanim to bless Israel. Thus we learn that first the Kohanim must be called, and only afterward do they begin blessing. If only one Kohen ascends the platform, "Kohanim" is not declared, since it is written, "Say to them" (in plural). Thus, the word "Kohanim" is only announced when there are at least two Kohanim present (Shulchan Aruch 128:10). Some authorities conclude that the essence of Birkat Kohanim is when there are at least two Kohanim to perform the blessing (Rabbeinu Peretz brought by the Tur 128; see Aruch HaShulchan 128:9).
The blessing itself is not recited by the Kohanim on their own. Rather, the chazan recites each word and the Kohanim repeat after him. Some chazanim mistakenly recite the words in a quiet voice. That is incorrect. Instead, the chazan's voice must be heard clearly by the Kohanim and should be just slightly softer than theirs (see Tzitz Eliezer 14:17; Nesiat Kapayim Kehilchatah 12:3.) Following each verse, the congregation answers Amen.
As we learned (in halachah 1) the awakening of our will to accept Hashem’s blessing awakens the Supreme Will to abundantly bestow blessing upon Israel. In other words, when HaKadosh Baruch Hu created the world, He established that free will was to be a key component. Therefore only after we awaken from below the desire for something positive, a parallel desire from Above awakens to aid us in achieving that thing. Hence, it is necessary that one of the Yisraelim being blessed first declares "Kohanim," thereby expressing in words our desire to accept Hashem’s blessing, and only then the Kohanim begin to bless. Afterwards as well, the chazan must read every word first, and in doing so, express our desire for every detail of the berachah, following which the Kohanim repeat that word, and HaKadosh Baruch Hu abundantly bestows His blessing upon us (Likutei Halachot LaMaharan, Nesiat Kapayim 3:4).
8.The Kohen’s Obligation to Remove His Shoes Before the Blessing
One of the nine enactments instituted by Rabbi Yochanan ben Zakai (who lived at the time of the destruction of the Second Temple) pertains to the law of Birkat Kohanim. He decreed that the Kohanim must not ascend the duchan to bless the nation while wearing sandals or shoes. There are a number of reasons for this enactment, one being out of respect for the congregation, for it is not appropriate for the Kohanim to bless the nation with mud on their shoes. Likewise, the Temple services were performed by the Kohanim without shoes, due to the sanctity of the site. The halachic reason for this enactment is that the laces of the Kohen’s shoes might become loose, causing him to feel uncomfortable standing on the duchan, which is a high place, where he can be seen by the whole nation. To hide his embarrassment, he would have to bend down and tie his laces, and the people might misinterpret his bending and not reciting Birkat Kohanim as his admission of not actually being a Kohen (Sotah 40a).
Based on these reasons, a Kohen may not ascend the duchan with shoes or sandals, nor with slippers that have laces. Regarding slippers, if they are made of leather, even without laces, it is prohibited to ascend the duchan in them as well, since ordinary shoes are generally made of leather, and all leather shoes are included in the enactment of Rabbi Yochanan ben Zakai. However, it is permissible to ascend the duchan in non-leather slippers that do not have laces.
In a place where it is not customary to appear barefoot, or in sandals without socks, before respectable people, it is proper that the Kohanim ascend the platform with socks on their feet (Mishnah Berurah 128:18). In a place where it is customary to walk in sandals without socks, even in front of respectable people, it is permissible for Kohanim to bless the people while barefooted (Olat Tamid 128:11).
At times, the question arises: what does a handicapped Kohen do if he is unable to take off his shoes, and likewise, what does a Kohen in the army do when he does not have time to remove his army boots? In cases of extenuating circumstances like these, some poskim are lenient and allow a Kohen to bless the people while standing on the floor of the synagogue, not ascending the duchan, where, because of its elevation, their feet and shoes can be seen, and this would bring disgrace to the blessing. If however, the Kohen is standing on the ground at the same level as the congregation, there is no prohibition to recite the blessing while wearing shoes. In extenuating circumstances, the Kohanim can rely on these poskim and bless Israel on the floor in shoes, provided that their shoes are clean (see Igrot Moshe, Orach Chaim, part 2, 32, regarding a handicapped person; concerning the issue of extenuating circumstances, see Tzitz Eliezer 14:11 and Yechaveh Da’at 2:13).