1 Samuel 24:20
And now, behold, I know well that thou shalt surely be king, and that the kingdom of Israel shall be established in thine hand. And now, behold, I know well that thou shalt surely be king, and that the kingdom of Israel shall be established in thine hand.
Saul himself conceded to David that he would surely become king and that the kingdom of Israel would be established in his hand. This admission came after David spared his life, when Saul recognized David's righteousness in showing him mercy and affirmed that the Lord would reward David for it. At that time David was only a shepherd youth holding nothing but God's promise of the throne, standing against Saul the reigning monarch who was determined to hold fast his power. Though utterly helpless in himself, David trusted God's word and withstood in Saul the power of the whole world, proving God's word stronger than human power and policy used in support of evil. By that trust he stands in the world's true nobility and royal line.