David went out wherever Saul sent him, [and] behaved himself wisely: and Saul set him over the men of war, and it was good in the sight of all the people, and also in the sight of Saul's servants.
Though he was just a very young fellow, he was set over a part of the army and these guys respected him so much, of course God's deliverance of the Philistine in his hand, that they just accepted him, but then trouble began to arise.