Albert Barnes Commentary Exodus 13:2

"Sanctify unto me all the first-born, whatsoever openeth the womb among the children of Israel, both of man and of beast: it is mine." — Exodus 13:2 (ASV)

Sanctify unto me - The command is addressed to Moses. It was to declare the will of God that all firstborn were to be consecrated to Him, set apart from all other creatures. The command is expressly based on the Passover.

The firstborn exempt from the destruction became in a new and special sense the exclusive property of the Lord: the firstborn of man as His ministers, the firstborn of cattle as victims. In place of the firstborn of men the Levites were devoted to the temple services.