Samuel said the Lord sent him to anoint Saul over His people and asked Israel to listen to God's words. Lord of Hosts said He would punish Amalek for setting himself against Israel while leaving Egypt. Samuel told Saul to utterly destroy and not spare Amalek, which pictured their separation from sin because of a holy God. He and the people spared Agag, the best of the sheep and all that was good. They only killed the despised and worthless (1 Sam. 15:1-9). God wants your whole heart in separating from sin and worshiping Him alone.
The Lord’s word came to Samuel saying he regretted making Saul king since he didn't follow God by carrying out His commands. Samuel was distressed and cried out to the Lord all night. Saul set up a monument for himself thinking he carried out the Lord’s command. Saul said the people spared the best of the sheep in sacrificing to Samuel’s god, but the rest were completely destroyed (1 Sam. 15:10-16). Total obedience glorifies God so you don't pursue selfish ambition, honor or convenience.
Samuel spoke to Saul what the Lord told him, “Though you were little in your own eyes; you were made head of tribes of Israel? And the Lord anointed you king over Israel, and the Lord sent you on a mission, and said, ‘Go and utterly destroy the sinners, the Amalekites, and fight against them until they are exterminated.' Why then did you not obey the voice of the Lord, but rushed upon the spoil and did what was evil in the sight of the Lord?” (1 Sam. 15:17-19). Humility enables you to obey God instead of seeking riches or glory for yourself.
Saul rationalized that he obeyed the Lord, but blamed the people for taking the choicest spoil to sacrifice to Him. Samuel said, “Has the Lord as much delight in burnt offerings and sacrifices as in obeying voice of Lord? To obey is better than sacrifice, and to heed than fat of rams. For rebellion is as the sin of divination, and insubordination as iniquity and idolatry. Because you rejected word of Lord, He has rejected you from being king” (1 Sam. 15:20-23). If you blame others for not obeying God's word and worship your service or success instead of Him alone, you become useless.
Saul confessed his sin against the Lord's command because he feared the people and listened to their voice. Samuel said the Lord tore Israel's kingdom from Saul and gave it to his neighbor who was better than him. God doesn't change His mind. Saul admitted his sin, but wanted honor from the elders before worshiping the Lord (1 Sam. 15:24-31). God acts according His word and can't use men-pleasers who seek honor as men-pleasers.
Samuel killed Agag, king of the Amalekites, who thought he was safe from being killed. Samuel grieved over Saul and did not see him until the day he died. The Lord regretted that He made Saul king over Israel (1 Sam. 15:32-35). Obeying God's word consistently ensures a vital ministry.
Because God loves a broken person, ask Him to reveal your stubbornness and self-will in following your own path in being successful. Like David who took Saul's place as king, confess your sin to God and ask Him to teach you the way you should go so His love will surround you (Ps. 32:5-10).