John Gill Commentary Numbers 3:6

"Bring the tribe of Levi near, and set them before Aaron the priest, that they may minister unto him." — Numbers 3:6 (ASV)

Bring the tribe of Levi near
Separate them from the rest, set them apart for special service about, the sanctuary, let them have a place nearer to it than the other tribes, or offer them, that is, to the Lord, as in (Numbers 8:11) ; as well as bring them near to Aaron; so it follows:

and present them before Aaron the priest ;
that he may receive them as a gift unto him, as servants to wait upon him; and! that he may appoint and declare unto them their work, and set them about it:

that they may minister unto him ;
in guarding the tabernacle taking care of the vessels of it, taking it down, carrying it, from place to place, and setting it up as there was occasion for it.