Saul said, I will give her to him, that she may be a snare to him, and that the hand of the Philistines may be against him. Therefore Saul said to David, You shall this day be my son-in-law a second time.
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.