Numbers 4:26

4:26 the hangings for the courtyard, the curtain for the entrance of the gate of the court, which is around the tabernacle and the altar, and their ropes, along with all the furnishings for their service and everything that is made for them. So they are to serve.

Numbers 16:9

16:9 Does it seem too small a thing to you that the God of Israel has separated you from the community of Israel to bring you near to himself, to perform the service of the tabernacle of the Lord, and to stand before the community to minister to them?

Numbers 18:7

18:7 But you and your sons with you are responsible for your priestly duties, for everything at the altar and within the curtain. And you must serve. I give you the priesthood as a gift for service; but the unauthorized person who approaches must be put to death.”