Albert Barnes Commentary 2 Samuel 24:2

"And the king said to Joab the captain of the host, who was with him, Go now to and fro through all the tribes of Israel, from Dan even to Beer-sheba, and number ye the people, that I may know the sum of the people." — 2 Samuel 24:2 (ASV)

1 Chronicles 21:2 supplies some missing words. This passage should read, as in 2 Samuel 24:4, And the king said to Joab and to the princes of the host who were with him, etc. (Compare to 1 Chronicles 27:22). They were employed with Joab as his assistants in the numbering, exactly as in the previous numbering in Numbers 1:4, when a prince was appointed from each tribe to be with Moses and Aaron.