Numbers 8:15

And after that shall the Levites go in to do the service of the Tabernacle of the Congregation, in performing their ministrations in the court and in transporting the Sanctuary from one station to the next; and thou shalt cleanse them, and offer them for an offering. These verses are a further explication of the preceding passage, for the Lord wanted it clearly understood what the position of the Levites was in the midst of the congregation.