11 And the Lord said to Moses, 12 "Behold, I have taken the Levites from among the people of Israel instead of every first-born that opens the womb among the people of Israel. The Levites shall be mine, 13 for all the first-born are mine; on the day that I slew all the first-born in the land of Egypt, I consecrated for my own all the first-born in Israel, both of man and of beast; 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.