David, Goliath, and You: 1 Samuel 17

What does it mean that the Holy Spirit is on David? It means that he trusts the Word of the Lord over his own fears.
And God delivers Israel by delivering David; David's faith becomes Israel's faith.
Who, in this story, are we? David? No. We're the huddled, fearful, Israelites, waiting for a champion to be delivered and deliver us. That, we know, is Jesus. 
You are not David. Your problem is not Goliath. So you don't need to be a hero to be a healthy Christian. What do you need to do? Listen to the Word of the Lord regarding His Champion, King Jesus.