Not go forth. The soldiers saw that in this instance David’s presence with them would be more of a hindrance than a help. If the opposing army learned that David was with his men, every effort would be made against his person. If he could be slain, Absalom would have attained his purpose. So David was urged not to be present in the battle.
Thou art worth. In the majority of the Hebrew manuscripts the clause thus introduced reads literally, “For now like us [there are] ten thousand.” The translation of the KJV is obtained from the LXX, the Syriac, the Vulgate, and two Hebrew manuscripts. The difference between the two readings of this clause is only one letter in the Hebrew.
Out of the city. Taking his place in the city with the reserve forces, David would be in a position to take advantage of any turn of battle. If things went against his men, he would be able to send relief. Whatever turn the battle might take, the army would know that their commander was safe. His presence within the walls of the fortress would be a source of strength and inspiration to them as they fought, stirring them up to effort and bravery.