God chose the strong, capable Saul as Israel’s first king. Saul began his reign humbly and reverently.
However, over time, King Saul put his desires before God’s will and over Israel’s well-being. Saul’s reverence for God gradually diminished.
Once, Saul was instructed to wait seven days for the prophet Samuel to offer a sacrifice. But Saul was impatient, and he disobeyed God by offering the sacrifice himself.
Samuel pronounced God’s punishment for his deed in 1 Samuel 15:17, 23 (NASB), “…though you were little in your own eyes, you were made the head of…Israel…Because you have rejected the word of the LORD, He has also rejected you from being king.” Therefore, God anointed David as Saul’s replacement (1 Samuel 16:13).
Young David captured Saul’s attention when he killed Goliath. Saul initially approved of David, but later, he felt rivalry. As David became a mighty warrior, Jewish women, “sang to one another as they celebrated, ‘Saul has struck down his thousands, and David his ten thousands.’ And Saul was very angry… He said, "They have ascribed to David ten thousands, and to me they have ascribed thousands, and what more can he have but the kingdom?’” 1 Samuel 18:7-8. Saul felt threatened. Samuel 18:9 (NLT), “So from that time on Saul kept a jealous eye on David.”
1 Samuel 18:14, 15 (NLT) states, “David continued to succeed in everything he did, for the LORD was with him. When Saul recognized this, he became even more afraid of him. But all Israel and Judah loved David…”
As Saul’s selfishness increased, he didn’t always repent of evil actions. He sometimes made excuses rather than repenting. Saul even turned to the witch of Endor for counsel (1 Samuel 28:6,7).
However, David, seeking God’s favor, consistently, sincerely repented of his sins. David demonstrated loving God with all his heart, soul, strength and mind. David, though imperfect, was called a man after God’s own heart in Acts 13:22.
Saul’s persistence in following self-will rather than God’s will made his heart susceptible to jealousy toward David. Song of Solomon 8:6 (KJV) reads, “…jealousy is cruel as the grave…” Saul eventually committed suicide (1 Samuel 31:4). We can see what jealousy did to Saul.