Numbers 3:6

ושרתו אתו [BRING THE TRIBE OF LEVI … BEFORE AARON] THAT THEY MINISTER UNTO HIM — And wherein consists their ministering? ושמרו את משמרתו THAT THEY SHALL KEEP HIS CHARGE — Because the care of the Sanctuary, viz., that no stranger should approach it, was committed to his charge, as it is said, (Numbers 18:1) "Thou and thy sons, and thy father’s house with thee, shall bear the iniquity of the sanctuary”, (which Rashi explains to have reference to the iniquity committed by a “stranger” in approaching the holy things), and these Levites aided them — this therefore, was their ministering [alluded to here].

Bring the tribe of Levi near, and present them before Aharon the priest, that they may minister to him.

הַקְרֵב֙ אֶת־מַטֵּ֣ה לֵוִ֔י וְהַעֲמַדְתָּ֣ אֹת֔וֹ לִפְנֵ֖י אַהֲרֹ֣ן הַכֹּהֵ֑ן וְשֵׁרְת֖וּ אֹתֽוֹ׃