The Lord had rejected Saul as king and David was anointed. But he could not be king untill Saul had died. Saul and the Israelites assembled and camped in the Valley of Elah and drew up their battle line to meet the Philistines. The Philistines occupied one hill and the Israelites another, with the valley between them. So, as people lining up for war usualy did, they shouted at each other. Exept, the Israelites weren't shouting. Only Goliath. So you know the story. One thing that stuck out is that you could tell how confident David was in God. When Goliath said, " Am I a dog that you come at me with sticks?"
"You come against me with sword and spear and javelin, but I come against you in the name of the LORD Almighty, the God of the armies of Israel, whom you have defied. This day the LORD will hand you over to me, and I'll strike you down and cut off your head. Today I will give the carcasses of the Philistine army to the birds of the air and the beasts of the earth, and the whole world will know that there is a God in Israel. All those gathered here will know that it is not by sword or spear that the LORD saves; for the battle is the LORD's, and he will give all of you into our hands." He is completly counting on God to do anything.