David went forth to fight against Goliath (vv. 40-48). He took his staff, chose five smooth stones from the brook, and held his sling in his hand (v. 40). Goliath scorned him for being but a youth and considered that his coming to him was as one with staves coming to chase away a dog. Goliath then cursed David by his gods and said that he would give David's flesh to the birds of heaven and to the beasts of the field (vv. 41-44). David said to Goliath, "You come to me with sword and spear and javelin, but I come to you in the name of Jehovah of hosts, the God of the ranks of Israel, whom you have defied. On this day Jehovah will deliver you up into my hand; and I will strike you and remove your head from you. And I will give the corpses of the camp of the Philistines to the birds of heaven and to the animals of the earth on this day. And all the earth will know that there is a God in Israel; and all this congregation will know that it is not by sword or spear that Jehovah saves, for the battle is Jehovah's and He will deliver you into our hand" (vv. 45-47).
David killed Goliath and defeated the Philistines (vv. 49-54). He killed Goliath by slinging a stone into Goliath's forehead and beheading Goliath with his own sword (vv. 49-51a). The Philistines fled, and the men of Israel and Judah pursued them to slay them and plunder their camps (vv. 51b-53). David took the head of Goliath and brought it to Jerusalem, but he put Goliath's armor in his tent (v. 54).
David's victory over Goliath and the Philistines was a strong confirmation to God's choosing and anointing of him.
Saul found out that David, who held Goliath's head in his hand, was the son of Jesse the Bethlehemite (vv. 55-58).
What happened to David in chapters sixteen and seventeen was altogether under God's sovereignty. We all need to realize that because we are pursuing Christ today, every aspect of our environment is absolutely under God's sovereign hand. Eventually, those who defy the church life will be defeated. Therefore, we should trust in the Lord, have confidence in Him, and be at peace.