What does 1 Samuel 17:30 mean?

The Philistines and Israelites are at the Valley of Elah for war (1 Samuel 17:1–3). A giant Philistine champion, Goliath (1 Samuel 17:4–7), has challenged the Israelites to a winner-take-all duel (1 Samuel 17:8–10). The Israelites remain at the battlefield and form their lines daily, but they respond to this threat with great fear (1 Samuel 17:11, 24). Despite the offer of enormous reward (1 Samuel 17:25), no one is willing to take on the giant. In the midst of this, David has been sent by his father, Jesse, to bring food and check on his three oldest brothers who are with the Israelite army (1 Samuel 17:12–18). He hears Goliath's threats and inquires as to what will be done for the man who overcomes him. Goliath is a Philistine; Israel is the army of the living God (1 Samuel 17:26)—Israel need not live in this reproach.

David's oldest brother, Eliab, has come down on him in hot wrath for showing up to the battle and asking these apparently presumptuous questions (1 Samuel 17:28). Eliab seems to have been shamed and embarrassed by David's response to the situation. But David doesn't allow his brother's scolding to stop him from asking his questions. He just walks away and finds another group of soldiers to talk to. They tell him the same as he had heard before: The king will richly reward the man who succeeds in killing the Philistine champion (1 Samuel 17:25, 27).