I Samuel 17:33 And Saul said to David, Thou art not able to go against this Philistine to fight with him: for thou art but a youth, and he a man of war from his youth.
David is prepared to fight the giant because God has prepared him by giving him experience in battle. The other battles were minor compared to this one. He had killed the lion and bear in hand to hand combat. He had used the simple elements that his father and profession had placed in his hands. He grabbed him by his beard and struck him maybe with his rod or even his bare hand.
But the most important thing is that he knows full well that it wasn’t his power but the power of God that wrought the victory. It was the Lord that delivered him. It was the Lord that gave him the victory.
With his pastoral position had come the responsibility of protecting his sheep. He had done so risking his very life. He knew that all responsibility brings great risk. Now he hears a giant cursing his God.
He is responsible before God to defend His name. He knows that God is seeking someone who will stand for Him, David knows that if he will but be used God will in great power deliver him.
Now as a missionary or one preparing for missionary service you need to remember that you will have to fight the small battles before you can be used to topple the giant. In your local church begin to kill the lions and bears now. Can you defeat your own laziness and lack of discipline? Can you stand for God and His man when others doubt, criticize and do not do their responsibility?
You need not consider going over seas to win souls and disciple believers until you are successfully doing so where you are. If you can not manage the money that you now have for His honor and glory do not expect Him to give you more. Do you pay your bills on time? Are you are man of your word.
Be faithful in the little things before you expect God to trust you will the big things:
Luke 16:10 He that is faithful in that which is least is faithful also in much: and he that is unjust in the least is unjust also in much. 11 If therefore ye have not been faithful in the unrighteous mammon, who will commit to your trust the true riches? 12 And if ye have not been faithful in that which is another man’s, who shall give you that which is your own?