On the day that Samuel anointed Saul, “God gave him another heart.” (1 Samuel 10:9) Saul's first act was rallying Israel to defend the people and city of Jabesh from the Ammonites. The Spirit of the Lord came on Saul, and with passion, he called all able men of Israel to arms. With one accord, 330,000 responded. Saul organized the troops into three companies, and attacked and defeated the Ammonites.
After two years, Saul took a small army against the Philistines, and his son, Jonathan, attacked one small garrison. This was enough to aggravate the Philistines to gather a massive army of men and equipment to retaliate. The Israelites panicked, and many abandoned their posts. In an impatient attempt to secure God's blessing, Saul offered a sacrifice before Samuel arrived, something prohibited by God's law. When Samuel came, he foretold the end of Saul's reign as king, and that God would seek a new king.
Saul began making dreadful decisions, including forbidding his fatigued and disillusioned army to eat, even condemning his son to death, a verdict not supported by the people whose lives Jonathan had saved. Jonathan also knew that his father was becoming problematic for Israel. With Saul's failure to carry out God's commands to annihilate the Amalekites, Samuel pronounced God's extreme displeasure and the end of Saul's reign. The Spirit of the Lord departed from Saul, and an evil spirit began to trouble him. The Philistines, also, were relentless in their harassment of Israel. When Saul heard that David had acquired food from Ahimelech, a priest in Nob, he called Ahimelech and 85 other priests to a meeting, and accused them of conspiracy. Saul murdered them all, and then slaughtered everyone in Nob: men, women, children and animals.
When David conquered Goliath, he instantly won the allegiance of the Israelites. Jonathan and David became close friends, but with David's success and popularity, Saul was insanely jealous. Saul knew God's Spirit was no longer with him, and he was afraid of David. Although David was loyal to Saul, Saul hated him, and began to deliberately send David into difficult military assignments, hoping he would be killed, but David always succeeded. In moments of right-mindedness, Saul loved David, but plagued by evil spirits, Saul continued to pursue David to murder him, driving him into hiding.
In order to hunt David, Saul abandoned all of his royal duties. One day, when David and his men were hiding in a cave, Saul came in to relieve himself. David had the perfect opportunity to kill Saul, but would not touch the Lord's anointed. He silently cut off part of Saul's robe. After Saul left the cave, David called out, revealing his life-sparing actions. Moved by David's words, Saul called off the pursuit. David, knowing Saul's mercy was temporary, lived in the wilderness. As expected, Saul resumed his manhunt, and came with 3,000 men to the wilderness of Ziph. While Saul slept, David had another chance to kill him, but again spared his life. David took Saul's spear and a flask of water, and the next day addressed Saul from a nearby hill. Saul realized what David had done, and again repented and went home. David went to live in the land of the Philistines.
When the Philistines assembled against Israel, Saul inquired of the Lord, but the Lord was silent. Saul's choice to seek out counsel from a witch or spirit medium proved to be a fatal error. He went to Endor, and met with a woman, requesting that she bring up the spirit of Samuel. The spirit predicted Saul's impending death and defeat for the armies of Israel.
The Philistine invasion was successful, and Saul's sons, including Jonathan, were killed. Saul was wounded, and when his armorbearer refused his order to kill him, Saul fell on his own sword, and the armorbearer also did the same. The Philistines hung Saul's headless body on a wall. The men of Jabesh, whom Saul had rescued many years before, journeyed through the night and removed the headless bodies of Saul and his sons from the city wall. They took them to Jabesh where they cremated and buried them.
“'So Saul died for his unfaithfulness which he had committed against the LORD, because he did not keep the word of the LORD, and also because he consulted a medium for guidance. But he did not inquire of the LORD; therefore He killed him, and turned the kingdom over to David the son of Jesse.'” (1 Chronicles 10:13, 14)