In Israel it is common practice for kohanim to bless the congregation on a daily basis towards the end of the repetition of the Amida prayer. In the Diaspora it is a much less frequent occurrence, which takes place only on the festivals of Pesaḥ, Shavu’ot and Sukkot, as well as on the High Holy Days.
The Mishna teaches that a kohen whose hands are disfigured should not participate in this blessing; according to Rabbi Yehuda if someone’s hands are colored with dye he too should not participate, as it will be distracting to the congregants. Although the popular notion is that it is forbidden to look at the hands of the kohanim while they are offering the blessing, since the Sages teach that the presence of the Almighty appears there at that time, the rishonim already have noted that the sense of Divine presence during the Priestly Blessing is only true in the Temple. Thus, the Meiri and Rid – echoing the Talmud Yerushalmi – explain that the concern here is that the congregants may be distracted from paying attention to the berakha. Based on this, we find the ruling of the Rema in the Shulḥan Aruk (Orah Hayyim 128:30) that if the local custom requires the kohen to cover himself with a tallit during the blessing, the restrictions of the Mishna would not apply.
Other limitations which may restrict kohanim from participating in the blessing include those whose pronunciation of the blessing is less that perfect. The baraita teaches that the people of Beit She’an, Beit Haifa and Tivonin were not permitted to bless the people because they could not distinguish between the pronunciation of the letter aleph and the letter ayin.
Unlike the people who grew up in the southern part of Israel, people who were raised in the Galilee – and, apparently, in particular cities in the Galilee where there was a large non-Jewish population – did not learn proper Hebrew pronunciation. Guttural sounds with origins in the throat – like the letters ayin and het – were difficult for those who grew up in places where languages other than Hebrew were prevalent.