Now the children of Israel after their number, the heads of fathers' [houses] and the captains of thousands and of hundreds, and their officers who served the king, in any matter of the divisions which came in and went out month by month throughout all the months of the year--of every division were twenty-four thousand.
Apparently, this arrangement continually surrounded David with 24,000 armed men, month by month, and made available for any emergency the entire 288,000.  It also left the soldiery practically free eleven months in the year to pursue their own interests.  The monotonous repetition is characteristic of ancient records and denies the notion that "The Chronicler" invented these records.