The teller of this story is far more clever and subtle than the translators allow. Whenever Goliath moves in the combat phase of the tale, it takes him fully three verbs to do so! This is so both at 1 Samuel 17:41 and 48, though translations disguise the fact. David, on the other hand, always moves quickly toward the line of battle, staying well out of reach of that deadly spear. Goliath expects to make short work of this runt, but before he can lumber his way to employ spear or sword, David has placed a stone in his shepherd's sling, a weapon he has surely used before, and fells the monster with one well-aimed shot. Goliath falls face down in the river, and before his death, David grabs his giant's sword and saws off his enormous head, holding it high as a sign of the complete victory.
It has long been said that David has won this fight solely through the power and presence of YHWH, but that is simply not true. David looked at Goliath, saw his heavy chain mail and his heavy spear and knew that he had the weapon that was needed, namely a mobile missile launcher. Goliath would be far too slow either to get close enough to David or to dodge the stone. Little wonder that David said he "used to keep sheep"; his destiny is to be king and Goliath will be his meal ticket to greatness.
The portrait of David here is the one we will see again and again in his fabulous story. He is immensely prepared to defeat whatever forces there may be to stand in his way to the kingship. Still there can be little doubt that David loves YHWH; it is just that at more times than not he loves himself and his desire for power more. Any people we know, any pastors we know who sound just like that?