Summary: The Philistines routed Israel in battle. Shaul kills himself rather than being captured alive. Upon hearing this news, the Jewish army fled and the Philistines plundered their cities. They removed Shaul’s head and took his armaments and stored it in their temple.
A deeper look: Shaul led the Jewish people into battle knowing that it would be his last. The Philistines began to rout Shaul’s men, targeting the king with archers (Samuel I 31:3). Shaul knew he was going to die in battle. Why then was he afraid of the archers (ibid.)?
Don Yitzchak Arbravanel (d. 1508) explains that Shaul was not afraid of dying, but of being injured and captured. If the Philistines took him alive they might parade him and desecrate God’s Name. This is why Shaul ordered his armour-bearer to kill him (Samuel I 31:4). Yet the amour-bearer refused, fearing that even under those circumstances, it would be a great transgression to kill the anointed king of Israel. So Shaul took the sword and fell upon it, killing himself before the Philistines could take him (ibid.).
While the Torah prohibits suicide (Genesis 9:5) many commentators demonstrate that under these extraordinary circumstances, Shaul was right to kill himself. Rabbi David Kimchi (d. 1235) notes that Shaul knew through Samuel’s prophecy that he was going to die anyway. It was better to die by his own hand than be mocked and tortured to death by the Philistines (Radak on Samuel I 31:4).
After Shaul’s death together with his sons and armour-bearer, the Philistines took Shaul’s body, decapitated it and placed his remains ‘on the wall of Beth-shan’ (Samuel I 31:10). They took his head and placed it in the temple of Dagon, a Philistine idol. Rabbi Meïr Leibush ben Yehiel Michel Wisser (d. 1879) explains that this was to exact revenge for the damage done to Dagon when the ark had been captured and taken there (Samuel I 5:1-8).
The inhabitants of Yavesh-Gilaad heard that Shaul’s body had been taken. They launched a daring attack to reclaim Shaul’s remains and afford him and his sons a proper burial.
While Shaul had made many mistakes, he was a righteous man and his loss was a great tragedy for the Jewish people. The baton of kinship now passed to King David. Shaul’s era had ended and David’s had begun, thus completing the First Book of Samuel.