Numbers 18:3-9

³And they shall keep thy charge, and the charge of the whole tent: only they shall not come near to the vessels of the sanctuary and to the altar, that they may not die, and you as well as they.

⁴And they shall unite with thee, and keep the charge of the tent of meeting, for all the service of the tent; and no stranger shall come near to you.

⁵And ye shall keep the charge of the sanctuary, and the charge of the altar; that there come no wrath any more upon the children of Israel.

⁶And I, behold, I have taken your brethren, the Levites, from among the children of Israel; to you are they given as a gift for Jehovah to perform the service of the tent of meeting.

⁷But thou and thy sons with thee shall attend to your priesthood for all that concerneth the altar, and for that which is inside the veil; and ye shall perform the service: I give you your priesthood as a service of gift, and the stranger that cometh near shall be put to death.

⁸And Jehovah spoke to Aaron, And I, behold, I have given thee the charge of my heave-offerings, of all the hallowed things of the children of Israel; to thee have I given them, because of the anointing, and to thy sons by an everlasting statute.

⁹This shall be thine of the most holy things, reserved from the fire: every offering of theirs, of all their oblations, and of all their sin-offerings, and of all their trespass-offerings, which they render unto me, it is most holy for thee and for thy sons.