The Misva of Birkat Kohanim requires the Kohanim to bless the congregation each morning, raising their hands toward the congregation and reciting the special blessing text dictated by God to Moshe (Bamidbar 6:24-26).
The Gemara establishes in Masechet Ketubot (24b) that if somebody who is not a Kohen participates in Birkat Kohanim, giving the blessing like a Kohen, he is in violation of an affirmative Biblical command. The question thus arises as to whether it is permissible for somebody to bless somebody privately with this special Beracha. Many parents have the custom every Friday night to place their hands on the head of each child and bless him with Birkat Kohanim, and it is also customary at weddings for parents and grandparents to bless the bride and groom with Birkat Kohanim. Some Rabbis bless their students with this blessing, as well. Is this permissible if the person giving the blessing is not a Kohen?
The Kaf Ha’haim (Rav Yaakob Haim Sofer, Baghdad-Jerusalem, 1870-1939) writes (Orah Haim 128:8) that the prohibition applies only when a non-Kohen grants this blessing with the intention of blessing the people like the Kohanim. If his intention is simply to bless someone with these words, without usurping the role of a Kohen, then it is entirely permissible to bless with Birkat Kohanim.
Likewise, the Ben Ish Hai (Rav Yosef Haim of Baghdad, 1833-1909), in Parashat Re’eh (17), notes that in Baghdad, it was customary for the leading Rabbis to place their hands on a boy’s head at his Bar-Misva and recite Birkat Kohanim. This was done even by Rabbis who were not Kohanim.
Indeed, the Pahad Yishak (by Rav Yishak Lampronti, Italy, 1679-1756), in the "Beracha" section, emphatically supports the practice of blessing one’s children or students with Birkat Kohanim while placing both hands on their head. He adds that this is a proper practice according to the Sod (Kabbalistic teaching). The Yabetz (Rav Yaakob Emden, Germany, 1697-1776), in his commentary to the Siddur, also supports this practice, emphasizing that parents should bless their children with both hands, and adding that this was the custom of his father, the Hacham Sevi (Rav Sevi Ashkenazi, 1656-1718).
It is thus entirely permissible, and appropriate, for even a non-Kohen to bless someone with Birkat Kohanim, so long as he does not intend to bless like a Kohen.
Summary: It is forbidden for a non-Kohen to participate in the Birkat Kohanim in the synagogue. However, a non-Kohen is allowed to privately bless somebody – such as a student, a child or a grandchild – with the text of Birkat Kohanim, while placing both hands on the person’s head.
