Numbers 1:51

1:51 Whenever the tabernacle is to move, the Levites must take it down, and whenever the tabernacle is to be reassembled, the Levites must set it up. Any unauthorized person who approaches it must be killed.

Numbers 18:2

18:2 “Bring with you your brothers, the tribe of Levi, the tribe of your father, so that they may join with you and minister to you while you and your sons with you are before the tent of the testimony.