Charles Ellicott Commentary Numbers 18:2

"And thy brethren also, the tribe of Levi, the tribe of thy father, bring thou near with thee, that they may be joined unto thee, and minister unto thee: but thou and thy sons with thee shall be before the tent of the testimony." — Numbers 18:2 (ASV)

That they may be joined to you.— There is an allusion here to the meaning of the name Levi, which was given to Leah’s third son. (See Genesis 29:34.) The Hebrew verb is the same as that which occurs in the speech of Leah.

And minister to you: but you and your sons ... — Or, and they shall minister to you, both to you and to your sons with you, before the tent of witness. The service of the Levites was executed before the tent— i.e., in the court; that of the priests was in the holy place, as well as in the court (Numbers 18:7).