1 Samuel 17
And there came out from the camp of the Philistines a champion named Goliath of Gath, whose height was six cubits and a span.  He had a helmet of bronze on his head, and he was armed with a coat of mail, and the weight of the coat was five thousand shekels of bronze.  And he had bronze armor on his legs, and a javelin of bronze slung between his shoulders.  The shaft of his spear was like a weaver's beam, and his spear's head weighed six hundred shekels of iron. And his shield-bearer went before him.  He stood and shouted to the ranks of Israel, “Why have you come out to draw up for battle? Am I not a Philistine, and are you not servants of Saul? Choose a man for yourselves, and let him come down to me.  If he is able to fight with me and kill me, then we will be your servants. But if I prevail against him and kill him, then you shall be our servants and serve us.”  And the Philistine said, “I defy the ranks of Israel this day. Give me a man, that we may fight together.”  When Saul and all Israel heard these words of the Philistine, they were dismayed and greatly afraid...[full text]...
This list contains some of the resources that were used to prepare this sermon. Check them out if you want to dig a little deeper.
Dale Ralph Davis, 1 Samuel: Looking on the Heart
Sidney Greidanus, Preaching Christ from the Old Testament
Matt Chandler, "David, Goliath and the Gospel"
Tim Keller, "The Lord’s Anointed: 1 Samuel 16:1-13"