Numbers 18:3-9

³They will take care of your responsibilities and those relating to the Tent, but they must not come too close to the sacred objects of the sanctuary or the altar, otherwise they will die, and you will too.

⁴They are to help you and take care of the responsibilities of the Tent of Meeting, doing all the work at the Tent, but they are not allowed to be with you during your priestly ministry.

⁵You are to carry out the responsibilities relating to the sanctuary and the altar, so that my anger will not fall on the Israelites again.

⁶Look, I myself have chosen your brothers the Levites from the Israelites as my gift to you, dedicated to the Lord to do the work that relates the Tent of Meeting.

⁷But only you and your sons are responsible for your priesthood, doing all that concerns the altar and is behind the veil. Only you are to perform that service. I am giving you the gift of your priesthood, but anyone else who approaches the sanctuary must be executed.”

⁸The Lord told Aaron, “Listen, I have put you in charge of officiating at my offerings. All the holy contributions of the Israelites that they bring are reserved for you, and this is a permanent rule.

⁹Part of the most holy offerings taken from the burnt offerings are yours. Part of all the offerings they give me as most holy offerings, whether it's grain offerings or sin offerings or guilt offerings, that part belongs to you and your sons.