Why, &c. — Or, why should this be a cause of trespass, or an occasion of punishment to Israel? God commonly punishes the people for the sins of their rulers, because they are for the most part guilty of their sins in one kind or other; or at least God takes this occasion to punish people for all their sins.
Related Commentaries of 1 Chronicles 21:3
1 Chronicles 21:3
3 And Joab answered, The LORD make his people an hundred times so many more as they be: but, my lord the king, are they not all my lord's servants? why then doth my lord require this thing? why will he be a cause of trespass to Israel?