While it is not specifically stated, the text implies that Joab went with the first group. This is why it was necessary for him to choose someone else to be in command of the troops that would stay to fight the Ammonites. Instead of making the rest of his men the subject of the sentence, it will be more natural in many languages to turn the sentence around and say something like “he made his brother, Abishai, commander of the remaining forces” or “he appointed Abishai, his brother, to take control of the troops that he left behind.” Abishai was last mentioned in 3.30. In some languages it is necessary to specify whether Abishai was the younger brother or the older brother. Unfortunately the Hebrew text never indicates whether Joab or Abishai was older, but perhaps it may be assumed that Joab was the older, since he was the commander of David’s troops. It is also true that Joab is usually mentioned first where the two names occur together in lists.

He arrayed them: the pronoun here refers to Abishai and not to Joab. Once again the verb involves the arrangement of the military force in preparation for battle. Compare the similar expression in the two previous verses.

Quoted with permission from Omanson, Roger L. and Ellington, John E. A Handbook on the First and Second Books of Samuel, Volume 2. (UBS Helps for Translators). New York: UBS, 2001. For this and other handbooks for translators see here .