Numbers 3:5-8

And the Lord said to Moses, Make the tribe of Levi come near, and put them before Aaron the priest, to be his helpers, In order that they may be responsible to him and to all Israel for the care of the Tent of meeting, and to do the work of the House; And they will have the care of all the vessels of the Tent of meeting, and will do for the children of Israel all the necessary work of the House.