Then Saul clothed David with his armor. He put a helmet of bronze on his head and clothed him with a coat of mail, and David strapped his sword over his armor. And he tried in vain to go, for he had not tested them. Then David said to Saul, “I cannot go with these, for I have not tested them.” So David put them off. Then he took his staff in his hand and chose five smooth stones from the brook and put them in his shepherd's pouch. His sling was in his hand, and he approached the Philistine. (1 Samuel 17:38-40)
The worst interpretation of these verses would be, "march to the beat of your own drummer." A better interpretation would be, "don't put your faith in other people but in the Lord." David has not tested Saul's armor, but one thing he has tested well is his own faith in the Lord, and so he sticks with what has been tested. So should we not only be testing our own faith but trusting in the Lord above all else.
Trust in the Lord with all your heart,
and do not lean on your own understanding.
In all your ways acknowledge him,
and he will make straight your paths. (Proverbs 3:5-6)
It is better to take refuge in the Lord
than to trust in man.
It is better to take refuge in the Lord
than to trust in princes. (Psalm 118:8-9)
This is all true, but how do we put our faith in God? The worst thing we could do is try to conquer our Goliaths ourselves, believing that God is our source of power and strength, like an energy bar. We take the verse of Philippians 4:13 out of context:
"I can do all things through him who strengthens me."
But in context, see how the idea behind the verse changes:
I rejoiced in the Lord greatly that now at length you have revived your concern for me. You were indeed concerned for me, but you had no opportunity. Not that I am speaking of being in need, for I have learned in whatever situation I am to be content. I know how to be brought low, and I know how to abound. In any and every circumstance, I have learned the secret of facing plenty and hunger, abundance and need. I can do all things through him who strengthens me. (Philippians 4:10-13)
Now we see that what Paul is talking about is that Christ strengthens him to be content in all circumstances. He's not made into a superman by Christ. He is made content. Indeed, David is content in his circumstance. He doesn't take off Saul's armor shaking in fear, "what am I going to do now?" He has a plan, based on his experience, but his faith is so solid in the Lord that he does not fear. He is content in his circumstances.
So, if we are not to conquer our Goliaths ourselves, who is to conquer them? Well, the obvious answer is that Christ has already conquered them on the cross, and it is a deep, abiding, penitent faith in Christ that will not help us conquer our Goliaths but be content in the knowledge that Christ has already conquered them. Christ himself tells us not to be anxious, because anxiety is sin; it is a lack of faith in what Christ has done for us. We don't believe that he has succeeded on the cross. Many believe that Christ never existed. We have many hurdles to overcome in faith. But when one does believe in Christ and have full faith in him, what is that person desiring of Christ?
Remember the two gospels; the newer, false one and the old, true one. The new one is that of "helper" Jesus who is there for us, but we are our own saviors. The old one is that of Jesus as savior, us a sinners, and the reason for salvation being for the glory of God alone. We are not the center of the universe with God as our assistant. God is the center, and we are the instruments of his glory. Christ died to save the elect, so that God's loving kindness and mercy would be made manifest for all to see.
So, Christ is about to ascend in Acts 1, and this happens:
So when they had come together, they asked him, “Lord, will you at this time restore the kingdom to Israel?” He said to them, “It is not for you to know times or seasons that the Father has fixed by his own authority. But you will receive power when the Holy Spirit has come upon you, and you will be my witnesses in Jerusalem and in all Judea and Samaria, and to the end of the earth.” (Acts 1:6-8)
Jesus corrects the disciples, shifting the focus from this new gospel we attempt to form, back to the great, old gospel of faith. We are not to know the mind of God, but we are to proclaim the good news of Christ to the ends of the earth. We can only do this if we are content in all circumstances, like David, like Paul, like Christ. When we are discontent, we try hard to solve our own problems and beg God for help. When we have a true faith in Christ, we realize that God has already helped, on the cross, and our being content as a result enables us to do the good works that God has given us to do: sharing the gospel with our family, friends and neighbors.