Numbers 3-4
And the LORD spoke to Moses, saying, “Behold, I have taken the Levites from among the people of Israel instead of every firstborn who opens the womb among the people of Israel. The Levites shall be Mine, for all the firstborn are Mine. On the day that I struck down all the firstborn in the land of Egypt, I consecrated for My own all the firstborn in Israel, both of man and of beast. They shall be Mine: I am the LORD.”
Numbers 3:11-13
The LORD here hearkens back to the original Passover, reiterating His claim on all the firstborn, and substituting the entire tribe of Levi in place of those firstborn.
The LORD then asks for a census of the Levites, not those able to go to war, but every male from a month old and upward. I expect that our “numbers guy”, Fred, noticed that if we add up the Levite clans, we get 7,500 + 8,600 + 6,200 = 22,300, which is 300 more than the total of 22,000 given in Lev. 3:39. The traditional explanation of that “discrepancy” is that those 300 are themselves firstborn males and cannot do “double duty” by also serving as substitutes for non-Levite firstborns and so are subtracted out of the total. The census of non-Levite firstborn males gives a total of 22,273. As a result we end up with 273 “excess” non-Levite firstborns who have no one-for-one substitute and must therefore be redeemed at the price of 5 shekels of silver each.
In all of this the LORD confirms the ordination of the Levites for ministry and assigns them duties for the care of the Tabernacle and protection of the priests. But He is also protecting the people. He is calling the Levites to serve as mediators between a holy God and a not-so-holy populace.
In like fashion, we too need a Mediator. We too need a Substitute Who can take our place and can stand before God the Father, interceding for us, for we cannot approach this holy God on our own.
For there is one God, and there is one Mediator between God and men, the Man Christ Jesus, Who gave Himself as a ransom for all, which is the testimony given at the proper time.
I Timothy 2:5-6