Numbers 3:12 Now behold, I Myself have taken the Levites from among the children of Israel instead of every firstborn who opens the womb among the children of Israel. Therefore the Levites shall be Mine.
According to Exodus 13:2 all of the firstborn sons belong to God. It would seem that God’s original plan was that all firstborns were to serve as the priest of Israel. So, if that were the case, in light of the above scripture, what happened?
There is a story that says that at the time when Israel created and worshipped their golden calf that all of the tribes participated except for the tribe of Levite. Therefore, the Levites took the place of the firstborn.
But, it was not a smooth transfer. According to Numbers 18:15 the firstborn had to be redeemed for five shekels. There was a cost involved in buying back the firstborn from the Lord.
Joseph and Mary kept this command in Luke 2:22-24 and brought Jesus to be redeemed before the priests. The irony is that it was the priest who accepted His redemption from His parents and it was the priest, possibly the very same ones, who offered Him up as a sacrifice 33 years later as our redemption.