Saul started out with a lot promise and ended with a lot of problems, namely fear. Saul's whole kingship was marked by fear, he was constantly afraid and he let that fear define him. Instead of being the king God knew he could be, he became the king nobody thought he would be - a paranoid, ego-driven, self-serving king who broke his own laws. David is seen completely different, instead of fear defining David's reign, he let faith defend him - so God accomplished more through David because his faith than he could through Saul because of his fear. Fear keeps you FROM what faith keeps you FOR.