What does 1 Samuel 17:55 mean?
When this chapter is read out of context, it seems as if King Saul doesn't know who David is. Yet King Saul knew David prior to the encounter on the battlefield. David played music for Saul, and some think that the incident with Goliath was part of how David became the king's armor-bearer (1 Samuel 16:14–23; 17:15). The king approved David's request to go fight Goliath (1 Samuel 17:31–36) and even tried to loan David his armor (1 Samuel 17:38–40). Saul sent the young man out with a blessing, "Go, and the Lord be with you!" (1 Samuel 17:37). Seeing his courage, Saul asked for more information. This is much like the common moment in action movies where someone looks at the hero and asks, "who is this guy?"Saul probably did not remember whose family David came from. Saul "loved [David] greatly" (1 Samuel 16:21) and had previously asked David's father to send David into his service (1 Samuel 16:22). But that does not mean the king remembered every detail about each of his servants and their families. Now that he had special reason to pay attention to David, the king asks the commander of the army where the youth comes from.
It seems natural to want to know the origin of one so brave, courageous, and faithful to the Lord. The king had also promised to make any Israelite victor's family "free in Israel" (1 Samuel 17:25). Saul needed to know which household to thank and bless if David won. If David was killed, he also needed to know which family to notify.
Abner's response reveals the level of respect the king was given. He carefully gives his negative answer that he does not know David's origin by first saying "as your soul lives, O king."
First Samuel 17:55–58 depicts the meeting between King Saul and David immediately after David defeats the gigantic Philistine champion, Goliath. Saul has already met and employed David (1 Samuel 16:18–21); yet this victory has greatly increased the king's interest. Neither realize that this is the public beginning of a rivalry which will end in Saul's death and David's kingship. It will be God's judgment (1 Samuel 15:26), not any ambition from David (1 Samuel 24:9–11), which will bring down the jealous king (1 Samuel 18:7–9).
David, delivering food to his brothers at the Israelite army camp, hears the Philistine Goliath's defiant challenge. Single man combat could decide the battle, but no Israelite wanted to face the massive warrior. David is appalled that a Philistine would defy the armies of the living God. He volunteers to fight, and King Saul agrees. Before the battle, David declares that the Lord will give victory and thereby show the world that there is a God in Israel. David quickly kills and beheads Goliath. The Israelites chase the Philistines back to their own territory and plunder their camp. David brings Goliath's head to Saul.