The fourth, for the fourth month, was Joab’s brother Asahel, and his son Zebadiah was commander after him. There were 24,000 men in his division.
We have here an account of the regulation of the militia of the kingdom. David was himself a man of war, and had done great things with the sword; he had brought into the field great armies. Now here we are told how he marshalled them when God had given him rest from all his enemies.
Commenting on 1 Chronicles 27:1-15
Asahel--This officer having been slain at the very beginning of David's reign [Sa2 2:23], his name was probably given to this division in honor of his memory, and his son was invested with the command.
Asahel the brother of Joab - This verse proves that the division and arrangement mentioned above were made before David was acknowledged king in Hebron; for Asahel, the brother of Joab, who was fourth captain, was slain by Abner, while Ishbosheth reigned over Israel at Mahanaim, Sa2 2:19-23.