4 Bible Verses about Apostasy Of Saul

I will not return with you, Samuel answered. You rejected Jehovah's command. He has rejected you as king of Israel. Samuel turned to leave, but Saul caught hold of his cloak, and it tore. Samuel said to him: Jehovah has torn the kingdom of Israel away from you today. He gave it to someone who is a better man than you.read more.
The Glory of Israel does not lie or change his mind. He is not a mortal who changes his mind.

Saul was afraid of David, because Jehovah was with David but left Saul.

Samuel said to Saul: Why have you disturbed me? Why did you make me come back? Saul answered: I am in great trouble! The Philistines are at war with me. God has abandoned me. He does not answer me any more by prophets or by dreams. Please tell me what to do.

You disobeyed Jehovah's command and did not completely destroy the Amalekites. That is why Jehovah is doing this to you.