Numbers 8:18 (BSB)

But I have taken the Levites in place of all the firstborn among the sons of Israel.

From Numbers 8. Also in the ESV.

Commentary on Numbers 8:18

• Matthew Henry (Presbyterian), Matthew Henry's Complete Commentary on Numbers 8:5-26: We read before of the separating of the Levites from among the children of Israel when they were numbered, and the numbering of them by themselves (Num 3:6, Num 3:15), that they might be employed in the service of the tabernacle. Now here we have directions given for their solemn ordination (Num 8:6), and the performance of it, Num 8:20.
• John Gill (Reformed Baptist), Exposition of the Old and New Testaments on Numbers 8:18: And I have taken the Levites for all the firstborn of the children of Israel. Gave up his right in the firstborn, and instead of them took the Levites for his use and service: see Num 3:12. . Numbers 8:19 num 8:19 num 8:19 num 8:19And I have given the Levites as a gift to Aaron and his sons, from among the children of Israel,....
• Keil & Delitzsch (Lutheran), Biblical Commentary on the Old Testament on Numbers 8:12-19: Num 8:12-19 The Levites were then to close this transfer of themselves to the Lord with a sin-offering and burnt-offering, in which they laid their hands upon the sacrificial animals. By this imposition of hands they made the sacrificial animals their representatives, in which they presented their own bodies to the Lord as a living sacrifice well-pleasing to Him.