Let me share a story that will illustrate. In 1 Samuel 17, Saul is looking for someone to go against Goliath. Saul didn't believe David was up to the task; but listen to David's reply:
"But David said to Saul, 'Your servant used to keep sheep for his father. And when there came a lion, or a bear, and took a lamb from the flock, I went after him and struck him and delivered it out of his mouth. And if he arose against me, I caught him by his beard and struck him and killed him. Your servant has struck down both lions and bears, and this uncircumcised Philistine shall be like one of them, for he has defied the armies of the living God.' "
Why do you suppose David was given this extraordinary strength? Not because of any worldly credentials he had. He was given this strength because of what was in his heart—he desired to rescue his father's sheep from the mouth of the lion and the bear.