1Chr.10.13

So Saul died for his transgression which he committed against the LORD, even against the word of the LORD, which he kept not, and also for asking counsel of one that had a familiar spirit, to enquire of it;

1Chr.10.13

Saul died in disobedience, disobedient to GOD. He didn't obey GOD's words. Instead of praying, he went to a witch to seek guidance.

1Chr.10.13

Saul died because he was unfaithful to the LORD; he did not keep the word of the LORD and even consulted a medium for guidance,

1Chr.10.13

So Saul died for his unfaithfulness which he had committed against the LORD, because he did not keep the word of the LORD, and also because he consulted a medium for guidance.