1-chronicles 21:6

Levi and Benjamin counted he not - The rabbins give the following reason for this: Joab, seeing that this would bring down destruction upon the people, purposed to save two tribes. Should David ask, Why have you not numbered the Levites? Joab purposed to say, Because the Levites are not reckoned among the children of Israel. Should he ask, Why have you not numbered Benjamin? he would answer, Benjamin has been already sufficiently punished, on account of the treatment of the woman at Gibeah: if, therefore, this tribe were to be again punished, who would remain?

To omit the Levites would be to follow the precedent recorded in Numbers 1:47-49. The omission of Benjamin must he ascribed to a determination on the part of Joab to frustrate the king's intention, whereby he might hope to avert God's wrath from the people.

21:6 Counted not - Partly for the following reason; and principally by God's gracious providence to Levi, because they were devoted to hisservice; and to Benjamin, because they were the least of all the tribes,having been almost extinct, Judges 21:6 , and because God foresaw thatthey would be faithful to the house of David in the division of thetribes, and therefore he would not have them diminished. And Joab alsopresumed to leave these two tribes unnumbered, because he had speciouspretences for it; for Levi, because they were no warriors, and theking's command reached only of those that drew sword. And forBenjamin, because they, being so small a tribe, and bordering uponJerusalem, might easily be numbered afterward.