1 Chronicles 10

Philistines defeat Saul

Now the Philistines fought against Israel and killed many of them on Mount Gilboa as they ran away. The Philistines overtook Saul, and killed his sons: Jonathan, Abinadab, and Malchi-shua. The battle raged on against Saul, and the archers wounded him and tracked him down. Then Saul told his armor carrier, "Draw your sword and kill me with it so these ungodly people can't abuse me." But his armor carrier refused to do it because he was too scared. So Saul took his own sword and threw his body onto it. When his armor carrier saw that he was dead, he too threw himself on his own sword and died. That's how Saul died—he, his three sons, and his lineage died together. When all the Israelites in the valley saw that the army had retreated and that Saul and his sons were dead, they abandoned their cities and ran away, allowing the Philistines to come and inhabit them.

The next day, when the Philistines came to loot the dead, they found Saul and his sons dead on Mount Gilboa. They looted his body, cut off his head, took his armor, and sent messengers throughout the Philistines' country, proclaiming the good news to their idols and their people. They put his armor in their god's temple and displayed his head in the temple of Dagon. When all of Jabesh-gilead had heard what the Philistines had done to Saul, all their warriors took the bodies of Saul and his sons, and brought them back to Jabesh. They buried them under an oak tree in Jabesh and fasted for seven days.

So Saul died because he broke the faith. He severed trust with the Existing One by failing to keep the Existing One's command, and also by seeking guidance from a medium instead of from the Existing One. That's why the Existing One put him to death and handed over the kingdom of Jesse's son, David.