“When you take the census of the people of Israel, then each shall give a ransom for his life to the LORD when you number them, that there be no plague among them when you number them.
12. When thou takest the sum of the children of Israel. The tribute which God here demands at the taking of the census, is very fitly annexed to the First Commandment; for God, in making them tributary to Himself, shews that they were under His jurisdiction and power; and because He had purchased them to Himself, He willed that this voluntary gift of acknowledgment should be paid to Him.
Some observe that the repetition of those words, The Lord spoke unto Moses, here and afterwards (Exo 30:17, Exo 30:22, Exo 30:34), intimates that God did not deliver these precepts to Moses in the mount, in a continued discourse, but with many intermissions, giving him time either to write what was said to him or at least to charge his memory with it.
Commenting on Exodus 30:11-16
When thou takest the sum of the children of Israel, after their number,.... An account of them, how many they are; which was sometimes done, and was proper to be done, especially in time of war; though the present case seems to be for the sake of raising money for the tabernacle and the service of it: then shall they give every man a ransom...