Thematic Bible: Firstborn set apart as a

That you shall set apart unto the LORD all that opens the womb, and every firstling that comes of a beast which you have; the males shall be the LORD'S. And every firstling of a donkey you shall redeem with a lamb; and if you will not redeem it, then you shall break its neck: and all the firstborn of man among your children shall you redeem. And it shall be when your son asks you in time to come, saying, What is this? that you shall say unto him, By strength of hand the LORD brought us out from Egypt, from the house of bondage: read more.
And it came to pass, when Pharaoh refused to let us go, that the LORD slew all the firstborn in the land of Egypt, both the firstborn of man, and the firstborn of beast: therefore I sacrifice to the LORD all that opens the womb, being males; but all the firstborn of my children I redeem. And it shall be for a sign upon your hand, and for frontlets between your eyes: for by strength of hand the LORD brought us forth out of Egypt.