Numbers 8:19

Bring the tribe of Levi near, and present them before Aaron the priest, that they may minister unto him. And they shall keep his charge, and the charge of the whole congregation before the tabernacle of the congregation, to do the service of the tabernacle. And they shall keep all the instruments of the tabernacle of the congregation, and the charge of the children of Israel, to do the service of the tabernacle. And thou shalt give the Levites unto Aaron and to his sons: they are wholly given unto him out of the children of Israel.

And thy brethren also of the tribe of Levi, the tribe of thy father, bring thou with thee, that they may be joined unto thee, and minister unto thee: but thou and thy sons with thee shall minister before the tabernacle of witness. And they shall keep thy charge, and the charge of all the tabernacle: only they shall not come nigh the vessels of the sanctuary and the altar, that neither they, nor ye also, die. And they shall be joined unto thee, and keep the charge of the tabernacle of the congregation, for all the service of the tabernacle: and a stranger shall not come nigh unto you. And ye shall keep the charge of the sanctuary, and the charge of the altar: that there be no wrath any more upon the children of Israel. And I, behold, I have taken your brethren the Levites from among the children of Israel: to you they are given as a gift for the LORD, to do the service of the tabernacle of the congregation.

Because their office was to wait on the sons of Aaron for the service of the house of the LORD, in the courts, and in the chambers, and in the purifying of all holy things, and the work of the service of the house of God; Both for the shewbread, and for the fine flour for meat offering, and for the unleavened cakes, and for that which is baked in the pan, and for that which is fried, and for all manner of measure and size; And to stand every morning to thank and praise the LORD, and likewise at even: And to offer all burnt sacrifices unto the LORD in the sabbaths, in the new moons, and on the set feasts, by number, according to the order commanded unto them, continually before the LORD: And that they should keep the charge of the tabernacle of the congregation, and the charge of the holy place, and the charge of the sons of Aaron their brethren, in the service of the house of the LORD.

Yet they shall be ministers in my sanctuary, having charge at the gates of the house, and ministering to the house: they shall slay the burnt offering and the sacrifice for the people, and they shall stand before them to minister unto them. Because they ministered unto them before their idols, and caused the house of Israel to fall into iniquity; therefore have I lifted up mine hand against them, saith the Lord GOD, and they shall bear their iniquity. And they shall not come near unto me, to do the office of a priest unto me, nor to come near to any of my holy things, in the most holy place: but they shall bear their shame, and their abominations which they have committed. But I will make them keepers of the charge of the house, for all the service thereof, and for all that shall be done therein.