John Gill Commentary 2 Samuel 18

And David numbered the people that [were] with him
Which Josephus says ^F4 were four thousand; but one would think there should be more by what follows:

and set captains of thousands and captains of hundreds over them ;
he divided his army into companies, which consisted some of a thousand and others of a hundred; over each of which he set captains, to lead them on, direct, and command them in battle.

FOOTNOTES:

• F4: Antiqu. l. 7. c. 10. sect. 1.

And David sent forth a third part of the people under the hand
of Joab
Very likely that which made the centre of the army, since Joab was the general of the army; though this distribution was made when David thought to have headed the army himself, and so made with respect to that:

and a third part under the hand of Abishai the son of Zeruiah, Joab's
brother ;
who was next to Joab in the army, and fought with him against the Syrians and Ammonites, (2 Samuel 10:10 2 Samuel 10:11) ;

and a third part under the hand of Ittai the Gittite ;
of whom see (2 Samuel 15:19) ; of these two parts consisted the right and left wings of the army:

and the king said unto the people ;
the soldiers, and particularly the officers:

I will surely go forth with you myself also ;
in which he seemed very resolute and peremptory; and this he proposed to do, not merely to animate the soldiers with his presence, and to show that he was willing to hazard his life with them, but chiefly for the sake of Absalom, to preserve his life, if possible.

But the people answered, thou shalt not go forth They were as resolute as David:

for if we flee away, they will not care for us ; to pursue after us;

neither if half of us die, will they care for us ; they will make no account of the victory; but if they could slay David, or get him into their hands, it would be more to them than if the whole army was routed:

but now [you are] worth ten thousand of us ; not only in our own esteem, but in the account of the enemy, who had rather you should fall into their hands than ten thousand of us; and as the advantage to them, so the loss to us would be more than ten thousand men:

therefore now [it is] better that you succour us out of the city ; either by sending them provisions or recruits, that might be there in reserve, if necessary; or by being ready to receive them into it should they be repulsed; or rather by his prayers to God for them; so the Targum,``now it is better that you pray for us out of the city;'' that is, that the Lord would help us; and so most of the Jewish commentators understand it of helping them by his prayers and counsels.

And the king said to them, what seems best to you I will do ,
&c.] Which was an instance of great condescension in him; and it was his wisdom and prudence to yield to them at such a time as this, and especially as their sentiments were founded on affection and loyalty to him:

and the king stood by the side of the gate ;
of the city of Mahanaim:

and all the people came out by hundreds, and by thousands ;
and passed by him, to whom no doubt he gave his blessing and best wishes; and, as Abarbinel thinks, now it was he composed and said the twentieth psalm, "The Lord hear thee in the day of trouble" (Psalms 20:1–9) .

And the king commanded Joab, and Abishai, and Ittai
His three generals, to whom he had committed his army divided into three parts:

saying, [deal] gently for my sake with the young man, [even] with
Absalom ;
he does not call him his son, being in rebellion against him, but the young man, who was young, and rash, andfoolish, and so to be pitied; his request is, that they would spare him, and not take away his life, when intheir power; that they would not aim at him, and push him hard, and fall upon him with wrath and fury; but ifhe fell into their hands, to take him alive, and bring him away, and not put him to death. This flowed from anatural affection to him, and a concern for the welfare of his soul, that he might not die in this sin; andalso from a consciousness that it was for his own sins that he was raised up to rebel against him; and heseems to speak as if he was certain that the battle would go for him, and against Absalom; and which he mightconclude from the answer of prayer he had in defeating the counsel of Ahithophel:

and all the people heard when he gave all the captains charge
concerning Absalom ;
not only the three generals, but all the captains of hundreds and thousands, and this was heard by the commonsoldiers as well as by the people of the city that were spectators on this occasion, see (2 Samuel 18:12).