Exodus 13:12
That thou shalt set apart unto the LORD all that openeth the matrix, and every firstling that cometh of a beast which thou hast; the males shall be the LORD’s. That thou shalt set apart unto the LORD all that openeth the matrix, and every firstling that cometh of a beast which thou hast; the males shall be the LORD’s.
This command belongs to the history of the children of Israel recorded in Exodus 13-16. At that time Jesus Christ, enshrouded in the pillar of cloud, led Israel as a mighty General of armies. His angels carried out His commands on either side of the vast army of more than a million people so that no harm could come to them. He made a passage through the Red Sea with the waters standing as a wall on the right hand and on the left and the cloud standing as a wall of fire between Israel and the Egyptians.
It requires that every male firstling of the beasts be set apart as belonging to the Lord. The firstborn son was likewise consecrated to God, but a redemption price was paid for him.