Then said Saul, I have sinned: return, my son David; for I will no more do you harm, because my life was precious in your eyes this day: behold, I have played the fool, and have erred exceedingly.
So David is sort of chiding Abner the chief general of Saul, saying, "Hey you know your job is to guard the king, and you aren't doing a good job. You ought to be put to death. Someone came in to destroy the king, and you were just sound asleep. Look where the king's spear is, and the cruse of water."