Halachos
1. It is essential that Kohanim, who give a bracha to Hashem’s nation, know the halachos of Birkas Kohanim well to be able to fulfill the mitzva with the proper care and precision. It is equally vital for Yisre’eilim receiving the bracha to know the halachos, as many points apply to them—how to receive the bracha, how to call out the bracha to the Kohanim, in which places is the minhag to do Birkas Kohanim, etc. Thus, we set forth here the common and applicable halachos so that Kohanim will give the bracha properly and Yisre’eilim will receive the bracha properly.
The Mitzva
2. For the Kohen. It is a mitzvas asei d’oraisa for Kohanim to bless Bnei Yisroel with uplifted hands (גמ' סוטה דף ל''ח ע''א, רמב''ם פט''ו תפילה הי''ב ), as the posuk says (פ' נשא ו', כ''ג ), “כה תברכו את בני ישראל אמור להם, יברכך ה' וישמרך, יאר וכו'.” Hashem, in His great goodness, wanted His nation to get a bracha specifically through the Kohanim, as they are constantly in the house of Hashem; their thoughts are completely attached to His avoda; and their souls are bound to His yirah all day. In their zechus, the bracha will take effect on them; all their actions will be blessed; and the pleasantness of Hashem will be on them (חינוך מצוה שע''ח ).
3. For the Yisroel. Some say that just as the Kohen has a mitzva to give the bracha, the Yisroel has a mitzvas asei to receive the bracha (ס' הפלאה כתובות כ''ד ע''ב בשם ס' חרדים, שו''ת חת''ס או''ח סי' כ''ב, באור הלכה ריש סי' קכ''ח ). However, some hold it is not a full mitzvas asei, but there is an element of mitzva for the Yisroel receiving the bracha too (שו''ת מהרש''ם ח''ח סי' כ''ה ).
Nowadays
4. D’rabanan. Some say that now that there is no Beis HaMikdash, mid’oraisa this mitzva does not apply; it is only d’rabanan. This is either because the chiyuv d’oraisa is only when the Shem HaMeforash is said, as it was in the Beis HaMikdash (ישועות יעקב אבהע''ז סי' ג') or because the yichus of Kohanim today is uncertain (מור וקציעה סי' קכ''ח, שו''ת בית אפרים או''ח סי' ו').
5. D’oraisa. However, most poskim hold it is a mitzva d’oraisa even today (שער הציון סוף סי' קכ''ח ).
Everywhere
6. Strictly speaking, the mitzva of Birkas Kohanim applies at all times and in all places (חינוך שע''ח ), even chutz l’aretz. However, for various reasons, many communities in chutz l’aretz today only do Birkas Kohanim at Mussaf of Yom Tov, as will be explained.
