As you and I face giants, we also must face ourselves. Giants come to intimidate. They stand before us and challenge us. These monsters create fear. They are overcome by trusting that God can overcome them. It takes faith.
God also uses small things to challenge us. Where big obstacles, like giants, make us question God's ability to overcome, insignificant things challenge us by forcing us to rely upon God and not our knowledge. The miracle is God's way of substantiating Himself by showing his sovereignty over the smallest of things.
The widow of Zarephath had to trust that God could produce enough from too little. It would take a miracle to accomplish such a task. Do you trust that God can do a great deal with very little?