Numbers 18:7

18:7 But you and your sons with you are responsible for your priestly duties, for everything at the altar and within the curtain. And you must serve. I give you the priesthood as a gift for service; but the unauthorized person who approaches must be put to death.”

Numbers 18:21-26

18:21 See, I have given the Levites all the tithes in Israel for an inheritance, for their service which they perform – the service of the tent of meeting. 18:22 No longer may the Israelites approach the tent of meeting, or else they will bear their sin and die. 18:23 But the Levites must perform the service of the tent of meeting, and they must bear their iniquity. It will be a perpetual ordinance throughout your generations that among the Israelites the Levites have no inheritance. 18:24 But I have given to the Levites for an inheritance the tithes of the Israelites that are offered to the Lord as a raised offering. That is why I said to them that among the Israelites they are to have no inheritance.”

Instructions for the Levites

18:25 The Lord spoke to Moses: 18:26 “You are to speak to the Levites, and you must tell them, ‘When you receive from the Israelites the tithe that I have given you from them as your inheritance, then you are to offer up from it as a raised offering to the Lord a tenth of the tithe.