The Torah sets out strict rules for the sacrifices that formed ancient worship and for those who were charged with the duty to offer those sacrifices. Just as any animal brought to the altar must be as near perfect as possible, so the kohen, the descendant of Aaron the High Priest who slaughtered that animal must be free of physical blemish. Leviticus chapter 21 goes into explicit detail. Blind, lame, hunchback, dwarf, cockeyed, scurvy, castrated these and other defects like a broken arm or leg disqualified a man for sacred service. He could eat his priestly portion. He could take part in upkeep of the sanctuary. He was still a kohen. He just could not officiate.
An interesting observation is what defects are not mentioned in this list. The three standard conditions that set people apart in all walks of life were deafness, insanity and underage. People in those conditions were not held responsible for carrying out most commandments. Our ancestors had no way to cope completely with the problem of how to teach the deaf, or to make the feebleminded or deranged understand. And of course an underage child changed status only on reaching the age of maturity. So these three do not appear here, and presumably it was taken for granted that they would not consider officiating at the altar.
In our day, with no sacrifices to offer, the kohen has much more limited duties. A very important one is the task and privilege of blessing the people. In Jerusalem this happens every day. Outside of Jerusalem it happens on select occasions, depending on the tradition of the community. Every Sabbath in some Sephardic congregations. (By contrast, many Ashkenazi congregations never have this ritual on Sabbath.) On Festivals and High Holy Days in all traditional synagogues. Do the Biblical restrictions apply to dukhenen, the act of pronouncing the Priestly Benediction? After all, the act requires each kohen to ascend in front of the Ark, and that could be difficult for a lame or blind man. Also he has to hear the cantor intone each word before he and the other kohanim repeat it to the people. His hands, spread in the traditional position with the ring finger and middle finger widely separated, have to hold his tallis out in front of him. Could he do that with a broken arm? No wonder the Talmud in Tractate Taanis states that a kohen who has a moom (a blemish) shall not raise his hands in blessing.
In fact, when the time comes for this blessing in many synagogues, we seldom see a handicapped kohen join in it.
Now wait a minute. We are not living in the days of the Talmud, and certainly not in the century of the Sanctuary. We have a different view of how to treat handicapped people today, and we dont call them blemished. There must be some way to open an opportunity for a blind or lame kohen to spread the Divine blessing. Suppose he is the only one available. Should his community not get blessed?
Well, the Code of Jewish Law, the famous Shulhan Arukh, anticipated that question, about 500 years ago. It sets out exceptions to the Talmudic edict. It states that if the kohen is well known in his community, so that the people will not be distracted by his handicap but will just listen to his blessing, then he is qualified to take part. And the standard of being well known is defined as living in that community for at least 30 days.
My friend Rabbi Binyomin Lisbon of my local Chabad synagogue tells me that Chabad encourages handicapped kohanim to perform the blessing, providing helpers for those who need them. Indeed Chabad favors fixing the place of people with disabilities in the very heart of the community, and allowing each and every person to take part in our shared effort to repair the world by the light of the Torah.
The one requirement that supercedes all others is found in the last word of the brocha that each kohen says before pronouncing the Benediction, praising G-d who has sanctified us with Aarons sanctity, and commanded us to bless the people Israel bahavah with love.
As a kohen, I am grateful for the opportunity to do that. And I can only encourage my fellow kohanim to join me, whatever blemishes we have.