Numbers 8:17 (BSB)

For every firstborn male in Israel is Mine, both man and beast. I set them apart for Myself on the day I struck down all the firstborn in the land of Egypt.

From Numbers 8. Also in the ESV.

Commentary on Numbers 8:17

• 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 8:17: For all the firstborn of the children of Israel are mine, both men and beasts,.... Not only in common with other of his creatures, but in a special respect on account of his signal deliverance of them; they were his, as Jarchi expresses it, by the line of judgment, or rule of justice and equity, because he protected them among the firstborn of the Egyptians...
• 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.