Exodus 13:2 - Joseph Benson’s Commentary on the Old and New Testaments

Sanctify That is, command all the people to sanctify; unto me To my use and service, in a manner I shall hereafter explain; all the firstborn That are males, as the command is limited, Exodus 13:12; whatsoever openeth the womb That is, every child which is the firstborn of his mother: so that if a man had many wives, either together or successively, his first child by every one of these was a firstborn, and, if a male, was claimed by the Lord. But if a female came first, and afterward a male, that male was not devoted to God, because it was not the firstborn. Hence the parents were not to look upon themselves as having an interest in their firstborn, if males, till they had first solemnly presented them to God, and received them back from him again. It is mine By special right and title, as being by singular favour preserved from the common destruction. The firstborn of man, if males, were claimed for the sacred ministrations of the priestly office. But after the Jewish commonwealth was formed, the Levites were chosen to officiate in their stead, Numbers 3:12; and the firstborn were to be redeemed at a certain rate, which was part of the priest's maintenance, Numbers 18:15-16. And of beast Which was to be offered to God, if a male: only an ass was to be redeemed.