11 Then the Lord spoke to Moses, saying: 12 I hereby accept the Levites from among the Israelites as substitutes for all the firstborn that open the womb among the Israelites. The Levites shall be mine, 13 for all the firstborn are mine; when I killed all the firstborn in the land of Egypt, I consecrated for my own all the firstborn in Israel, both human and animal; they shall be mine. I am the Lord.
Matthew Henry's Commentary on Numbers 3:11-13
Commentary on Numbers 3:1-13
(Read Numbers 3:1-13)
There was much work belonging to the priests' office, and there were 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 under further obligations to serve him faithfully. God's right to us by redemption, confirms the right he has to us by creation.