Numbers 3:8-10

Amplified Bible

⁸ They shall also take care of all the furnishings and utensils of the Tent of Meeting, and [attend to] the duties of the Israelites, doing the service of the tabernacle. ⁹ You shall give the Levites to Aaron and to his sons [as servants and helpers]; they are to be given wholly to him from among the Israelites. ¹⁰ So you shall appoint Aaron and his sons, and they shall observe and attend to their priesthood; but the layman (non-Levite) who approaches [the holy things] shall be put to death.”