John Gill's Bible Commentary Ver. 9. And thou shalt give the Levites unto Aaron and to his sons , etc.] To be their ministers and servants: they [are] wholly given unto him out of the children of Israel : even all of them entirely, none excepted; the whole tribe which were not in the priestly office; those were separated from the rest of the tribes of Israel, and appointed for the service of the priests: or they were “given, given” f16 ; which is repeated not only to show that they were wholly given, as we render it, but to denote the certainty of it, that they were really given; and especially to declare the freeness of the gift; the priests had them as free gifts, nor did they pay them any thing for, their service; they were maintained another way, namely, by the tithes of the people; and indeed the priests received a tithe out of the tithe of the Levites; so far were they from contributing any thing to their support, or in consideration of the service they did them.
Matthew Henry Commentary
Verses 1-13 - There was much work belonging to the priests' office, and there wer now only Aaron and his two sons to do it; God appoints the Levites to attend them. Those whom God finds work for, he will find help for. The Levites were taken instead of the first-born. When He that made us saves us, as the first-born of Israel were saved, we are laid unde further obligations to serve him faithfully. God's right to us by redemption, confirms the right he has to us by creation.
Original Hebrew ונתתה5414 את853 הלוים3881 לאהרן175 ולבניו1121 נתונם5414 נתונם5414 המה1992 לו מאת854 בני1121 ישׂראל׃3478