David is now the king-in-waiting. Although he has spent time with King Saul, David has now returned to the fields and his father's sheep. The Lord is still secretly preparing His servant in obscurity for great office. Saul's power is now waning and he is now being judged by the Lord who has sent a distressing spirit upon him. David is sent by his father on an errand that proves to be a defining moment in David's ascent to the throne. This battle with Goliath is what brings David to the attention of the people, including Saul, and is the proof that he is the Lord's anointed.
Let us consider the following: 1: The arrogance of the unbelieving world 2: The fear of the church 3: David's faith in God