6 But Joab did not include Levi and Benjamin in the numbering, because the king’s command was repulsive to him.

Read 1 Chronicles 21:6 Using Other Translations

But Levi and Benjamin counted he not among them: for the king's word was abominable to Joab.
But he did not include Levi and Benjamin in the numbering, for the king's command was abhorrent to Joab.
But Joab did not include the tribes of Levi and Benjamin in the census because he was so distressed at what the king had made him do.