King James Version (KJV)
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;
Modern English
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.
Hebrew
וַיָּ֣מָת שָׁא֔וּל בְּמַעֲל֖וֹ אֲשֶׁ֥ר מָ֖עַל בַּ֑יהוָה עַ֚ל דְּבַ֣ר יְהוָ֔ה אֲשֶׁ֥ר לֹא שָׁמָ֖ר וְגַ֕ם לִשְׁאוּ֖ל בָּאֽוֹב׃
vayamat shaʾvl bmaʿalvo ʾasher maʿal bayhvah ʿal dbar yhvah ʾasher loʾ shamar vgam lishʾvl baʾvob