1 Chronicles 10:13 So Saul died for his breach of faith. He broke faith with the Lord in that he did not keep the command of the Lord, and also consulted a medium, seeking guidance. 14 He did not seek guidance from the Lord. Therefore the Lord put him to death and turned the kingdom over to David the son of Jesse.
It's seems pretty clear. Saul died for breaking faith. He died because he didn't seek the Lord.
Lord, help me to seek You in all things for all my days.