Who says "Baruch ha'Ba b'Shem Hashem", and what does it mean?
Radak (29, citing Pesachim 119a): Shmuel said this when he anointed David.
Rashi: People will say so to those who bring Bikurim, or ascend [to the Mikdash] for the festival (they come b'Shem Hashem).
Radak: Kohanim in the Mikdash will say so to all who come to serve Hashem. You are blessed with Hashem's name.
Malbim: The Kohanim leave Beis Hashem to greet the king, and give to him Birkas Kohanim. Hashem already put His name on Bnei Yisrael - "v'Samu Es Shmi Al Bnei Yisrael", and they come to His Makdish with His name.
What is the meaning of "Beirachnuchem [mi'Beis Hashem]"?
Rashi: We blessed you. Malbim - the Kohanim say, we blessed you from Beis Hashem - the Brachah comes out of the house in which He dwells, and He blesses.