ישראל בני את תברכו כה לאמר בניו ואל אהרן אל דבר” (כג ו) “להם אמור
The Tosafos in Brachos (34a ad loc. Lo) brings in the name of the Midrash Chaseiros V’Yeseiros that the words “amor lahem” indicates that the shaliach tzibbur needs to read out each word of the brachah of Birchas Kohanim before the Kohanim say it in their brachah.
Why do the Kohanim have to bless the nation word for word from the shaliach tzibbur?
Rabbi Shlomo Hakohein of Vilna, author of Cheishek Shlomo, says that his brother Rabbi Betzalel Hakohein explained the reason for this halachah as follows:
In the passuk (Devarim 4:2) “Lo sosifu, do not add to the word that I have commanded and do not diminish from it.” The Torah instructs not to add to the way each mitzvah is fulfilled and not to detract from it. As such, the Kohein must be careful to bless Bnei Yisrael with the fifteen words mentioned in the Torah, not one word less or one word more (see Rosh Hashanah 28b). Therefore, in order to prevent the Kohanim from adding or subtracting a word inadvertently, the shaliach tzibbur has to read out to the Kohanim the brachah word for word.
This is what the Kohanim ask before their brachah: “Yehi ratzon, that this brachah that You commanded us to bless Your nation Yisrael should be a complete brachah, and there should be no obstacle or sin involved...” What is a “brachah sheleimah” and what sin could be contained in a brachah? Because the lack of one word leads the Kohanim to transgress “bal tigra”, they precede by asking that their brachah should be a complete brachah, not missing even one word, and this way their brachah should not involve any “michshol oh avon.”
Betzeila D’mehemnusa Chayei Sarah 5764
