Halakhah do Kapłańska 9:22

During Temple times, Birkat Kohanim would take place after the daily sacrificial offerings were completed. The Torah recounts that on the eighth day of the Mishkan’s dedication, the day that the kohanim were inaugurated in their service: “Aharon lifted his hands toward the people and blessed them. He then descended from [the altar where he] had prepared sin offering, burnt offering, and peace offering” (Vayikra 9:22). It is from here that we derive that Birkat Kohanim (also called “Nesi’at Kapayim” – “the lifting of the hands” – after this verse) took place at the conclusion of the sacrificial offerings. The reason for this is that after offering the sacrifices, which express our willingness to surrender and sacrifice ourselves for God, we are worthy of receiving His blessing.