What does 1 Samuel 17:14 mean?
Israelite and Philistine armies prepare for war (1 Samuel 17:1–3). An imposing and well-armored Philistine champion has challenged the Israelites to a winner-takes-all duel (1 Samuel 17:4–10). The Israelites are terrified. With that as a backdrop, the passage reintroduces David (1 Samuel 16). He is the son of an Ephrathite named Jesse who lives in Bethlehem (1 Samuel 17:12). David's three oldest brothers are at the battle (1 Samuel 17:13). David was the youngest of Jesse's eight sons.This fact was also highlighted in the previous chapter. After rejecting Saul as king, God told the prophet Samuel to go to Bethlehem to anoint the next king of Israel from Jesse's sons (1 Samuel 16:1). The Lord sequentially rejected seven of the sons of Jesse. So, Samuel asked if Jesse had any more boys (1 Samuel 16:5–10). The youngest was out in the fields watching the sheep, apparently not invited to participate in the feast with the rest of the family (1 Samuel 16:11). When young David finally arrived, the Lord confirmed to Samuel that this was His choice for Israel's next king. Samuel anointed the boy and the Spirit of the Lord came on David (1 Samuel 16:12–13). No mention is made of Samuel telling Jesse, David, or anyone else that the anointing was about becoming Israel's next king.
Shortly after this, David entered King Saul's service, helping ease the discomfort caused by a harmful spirit (1 Samuel 16:14–23). Evidently David went between tending sheep and helping the king (1 Samuel 17:15). It may even be that the brief description of David's service in the prior chapter (1 Samuel 16:21) included the fight with Goliath but saved the details for a separate account.