Numbers 18:6-8

I myself have chosen your fellow Levites from among the Israelites to be your special assistants. They are a gift to you, dedicated to the LORD for service in the Tabernacle. But you and your sons, the priests, must personally handle all the priestly rituals associated with the altar and with everything behind the inner curtain. I am giving you the priesthood as your special privilege of service. Any unauthorized person who comes too near the sanctuary will be put to death.” The LORD gave these further instructions to Aaron: “I myself have put you in charge of all the holy offerings that are brought to me by the people of Israel. I have given all these consecrated offerings to you and your sons as your permanent share.