Exodus 13:2

Sanctify unto me all the first-born— The Lord not only appointed an annual festival commemorative of his redemption of Israel, and ordained a weekly remembrance of it, Deuteronomy 5:15 but also commanded all the first-born of the males (Exodus 13:12 and Numbers 3:40.) to be sanctified; that is, (as the word קדשׁ cadesh always signifies,) to be separated, or set apart, from common and ordinary to higher and sacred uses. In this command, the reference to God's preservation of the first-born of Israel, when he destroyed the first-born of Egypt, is evident; see Exodus 13:15. The firstborn of man was to be dedicated to the Lord, set apart to the sacred ministrations of the priestly office. But it appears from Numbers 3:12 that the Levites were afterwards chosen instead of the first-born, who were to be redeemed at a certain rate, which was applied to the maintenance of the priests, Numbers 18:15. By this separation of the first-born is signified to us, that God's people, who are the congregation of the first-born, (ch. Exodus 4:22.Hebrews 12:23.) and are redeemed from death by the blood of Christ, should devote themselves as a living sacrifice, holy, acceptable unto God, which is their reasonable service. Romans 12:1.