The events of chapter 17 occur several years after David is invited to stay at King Saul’s residence. It appears that at some point, Saul’s condition must have improved and David was allowed to go back and help his father with his sheep.
In verses 1-3, we learn that the Philistines have assembled an army only 15 miles west of Bethlehem. The Israelites respond by amassing an army to confront the Philistines, and they both encamp facing each other across a valley, atop two ridges.
Rather than initiating a full-on assault of Israel, the Philistines elect to send their mightiest warrior, Goliath, down to the valley to invite a champion from Israel to face him in combat to the death. The losing side would surrender to the winning side and the battle would be avoided. This form of representative combat was not unknown in the ancient near east, although the Israelites rarely, if ever, practiced it. Goliath seems to have to explain to the Israelites how it will work in verses 8-11, which implies the Philistines were familiar with the concept and had even put it to use before.
Goliath is described as being almost 10 feet tall in some ancient manuscripts, and almost 7 feet tall in other manuscripts. Regardless of which is correct, the average Israelite soldier would have been about 5 feet tall, so Goliath would have seemed like a giant at either height. Goliath is dressed in the armor and weaponry of a heavy infantryman. Robert Bergen, in 1, 2 Samuel: An Exegetical and Theological Exposition of Holy Scripture (The New American Commentary)
Protecting his trunk was ‘a coat of scale armor weighing five thousand shekels’ (= 126 pounds). Completing his body armor were ‘bronze greaves’ (v. 6) or knee and shin protectors. A covering of this weight and composition would have drastically reduced Goliath’s ability to respond with quickness and agility in close combat and suggests that he did not expect a skirmish involving hand-to-hand combat.
Goliath’s weaponry was as overwhelming in appearance as his height and armor. He had ‘a bronze scimitar’ (Hb. kîdôn; NIV, ‘javelin’), a curved sword, ‘slung on his back.’ In addition, he had a spear whose ‘shaft was like a weaver’s rod.’ This description may relate to the size and weight of the spear’s shaft or, more probably, to the fact that it had a loop of cord attached to it. At the head of Goliath’s spear was a massive ‘iron point’ that weighed ‘six hundred shekels’ (= 15.1 lbs.). Iron was the preferred metal for implements of warfare because it was strong, nonmalleable, and could retain a sharp edge much better than bronze. A weapon of this massive weight, while intimidating in appearance, would have been quite awkward to use; it was apparently designed mainly to intimidate.
For forty days, the Israelites, led by King Saul, do not send a representative forward because they are scared and intimidated by Goliath. Meanwhile, young David, who is under the age of 20 and unable to serve in the military, is bringing supplies to his three brothers and their unit since Jesse’s home is only 15 miles away. When David arrives at the front lines with his supplies, he asks his brothers what is happening. They explain to him the situation and he is greatly upset that Goliath has been allowed to insult the God of Israel.
Due to his outspoken anger, David is invited to see King Saul, and he offers to fight Goliath himself. Saul counters that David is only a boy, but David explains that since God has been with him, he has been able to kill a lion and a bear who attacked his sheep. Saul relents and allows David to fight Goliath, hoping that God is still with David.
Rather than fight with Saul’s armor and sword, David decides to only bring his shepherd staff and a sling to the battle with Goliath. As David descends into the valley and approaches Goliath, Goliath mocks him and curses David in the name of David’s gods. Here is David’s response:
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.
For David, this is not just a military engagement, but a solemn religious duty. Leviticus 24:16 commands the death penalty for anyone who blasphemes God. Goliath had repeatedly blasphemed against God for 40 days, and did it yet again when David came to face him. This demonstrates one way is which David is a man after God’s heart, because he takes the words of the Torah (the Law) so seriously. In David’s mind, God Himself would help David carry out the commands of the Law.
In verses 48-51, we witness one of the quickest battles in the history of combat. As Goliath lumbers toward David, David runs toward Goliath, places a stone in his sling and whips it at Goliath’s head. The stone hits his forehead, breaking Goliath’s skull, and he drops dead. David takes Goliath’s own sword and decapitates him, making it clear to the Philistines that Goliath is dead.
Instead of honoring the deal they had made with Israel, the Philistine army turned and fled. The Israelites followed after them, chasing them back to their fortresses at Gath and Ekron. The Israelites then came back and plundered the camp that was abandoned by the Philistine army.
What happened to David after this great victory? Saul invited him to his home permanently, whereupon David and Saul’s oldest son, Jonathan became best friends. In fact, Jonathan symbolically cedes his right to the throne of Israel by giving David his robe, tunic, sword, bow, and belt.
Saul gives David a high rank in the army and whenever David goes out to fight, he is successful against his enemies. In fact, he is so successful that the women of Israel would chant, “Saul has slain his thousands, and David his tens of thousands.”
Saul becomes extremely jealous of David and in one episode at Saul’s house, Saul enters an ecstatic state and twice throws a spear at David with the intent to kill him. Both times he misses, however. From then on, Saul is constantly plotting how to ruin David. He sends him on numerous military campaigns, hoping he will die in battle, but David is always successful and is never harmed. For the next 10 chapters of 1 Samuel, Saul would plot to kill David and David would always escape.
The contrast between David, a man indwelt by the Spirit of God, and Saul, a man rejected by God, is illustrated over and over during the remainder of 1 Samuel. David wins battle after battle and Saul descends into madness as each day goes by.