כה תברכו את בני ישראל אמור להם (נשא ו:כג)

By the mitzvah of Birchas Kohanim (blessing of the priests), it says אמור להם – speak to them, versus “דבר להם” – talk to them.  Because the word “אמור” reflects אהבה – love.  The passuk teaches us that when one blesses another Yid he must have the middah – trait of אהבה – love for another Yid – just like he loves himself. And when one blesses another, it evokes mercy in heaven, bringing blessings to all.