The spiritual psycho-dynamic of David and Saul is given to us that we might understand the power and necessity of the Spirit-filled life.  As you may know, Saul was the first king of Israel accordind to the will of the people.  He was not God's choice.  The people wanted him as king because he tall and good-looking.  They did not consider character.  He did some good things , but for the most part he walked in the flesh and his life did not please God. David was God's choice.  He had the character that God desired for the ruler of his people, and God taught him much through Saul.