1 Chronicles 10:13

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,

Read 1 Chronicles 10:13 Using Other Translations

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;
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.
So Saul died because he was unfaithful to the LORD . He failed to obey the LORD ’s command, and he even consulted a medium

What does 1 Chronicles 10:13 mean?

John Gill's Exposition of the Bible
1 Chronicles 10:13

So Saul died for his transgression
(See Gill on 1 Samuel 31:13) A violent and dishonourable death, which was suffered on account of the sins he was guilty of:

one was, which he committed against the Lord, even against the word of
the Lord, which he kept not;
both in not staying for Samuel the time appointed, and by sparing the Amalekites whom he was bid to destroy, ( 1 Samuel 13:13 1 Samuel 13:14 ) ( 1 Samuel 15:3 1 Samuel 15:9 )

and also for asking counsel of one that had a familiar spirit, to
inquire of it;
what he should do with respect to engaging in battle with the Philistines, ( 1 Samuel 28:8 1 Samuel 28:15 ) which to do was contrary to an express command of God, ( Leviticus 19:31 ) .

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