Exodus 30:11-16

The Lord spoke to Moses: When you take a census of the Israelites to register them,¹ at registration all of them shall give a ransom for their lives to the Lord, so that no plague may come upon them for being registered.² This is what each one who is registered shall give: half a shekel according to the shekel of the sanctuary (the shekel is twenty gerahs), half a shekel as an offering to the Lord.³ Each one who is registered, from twenty years old and upwards, shall give the Lord’s offering. The rich shall not give more, and the poor shall not give less, than the half-shekel, when you bring this offering to the Lord to make atonement for your lives. You shall take the atonement money from the Israelites and shall designate it for the service of the tent of meeting; before the Lord it will be a reminder to the Israelites of the ransom given for your lives.

1 What would the point of taking a census be? To measure out your number for future war (the point is some Old Testament passage, but disavowed by God)? To ensure that all true Israelites were registered and accounted for? In order that people may be taxed appropriately?

2 Outside of the judgment in 2^nd Samuel, where the plague came upon the Israelites when David censused them disobediently, this statement would make little sense. Why would God send a plague upon them for participating in a census, especially one for which he has given the instructions? Lends credence to the thought that Exodus and Samuel were written up as part of a single community.

3 Even the census is tied specifically to an act of offering before the Lord.

Take-home: The instructions for the alter and its services are broken into to give instructions for a offering to be given during the census. This monetary offering reminds the Israelites that their lives are in God's hands.