Importance of the First Born

Numbers
3:13 Because all the firstborn [are] mine; [for] on the day that I smote all the firstborn in the land of Egypt I hallowed unto me all the firstborn in Israel, both man and beast: mine shall they be: I [am] the LORD


The dedication of the first-born had its origin in the earliest times. God had promised to give the First-born of heaven to save the sinner. This gift was to be acknowledged in every household by the consecration of the first-born son. He was to be devoted to the priesthood, as a representative of Christ among men. {DA 51.1}

Numbers 3:41 And thou shalt take the Levites for me (I [am] the LORD) instead of all the firstborn among the children of Israel; and the cattle of the Levites instead of all the firstlings among the cattle of the children of Israel.

The Firstborn are Freed by the levites

Numbers 3:50 Of the firstborn of the children of Israel took he the money; a thousand three hundred and threescore and five [shekels], after the shekel of the sanctuary:
Numbers 3:51 And Moses gave the money of them that were redeemed unto Aaron and to his sons, according to the word of the LORD, as the LORD commanded Moses.
According the above 2 verses the Israelites still had to pay redemption momey for their firstborn sons. Some people ion our church follow that practise