Verse 36 Also the first-born - See this law, and the reasons of it, Exo 13:1-13. As by this law the Lord had a right to all the firstborn, instead of these he was pleased to take the tribe of Levi for the whole; and thus the Levites served at the tabernacle and temple, instead of the first-born of all the tribes.

Neh 10:36

The first-born of our sons and of our cattle, as it is written in the law. See Exo 22:29; Exo 34:19. The firstborn children were to be "redeemed."