God regretted making Saul king. This story explains why. When God delivered the Israelites from Egypt, the Amalekites attacked their rear, taking out the stragglers when they were tired and weary. Worse, however, they did not fear God. In Exodus 17:14, God instructed Moses to write a memorial and to do it in the hearing of Joshua. “I will utterly blot out the remembrance of Amalek from under heaven.” A God of justice and One who fulfills His word, sent Samuel with instructions, to Saul, who acted, but caused God to regret His choice.

Instructions
Samuel had anointed Saul to follow God’s directions. The time had arrived for God to fulfil His promise to punish the Amalekites for their brutality to His people. Samuel relayed God’s message to King Saul. “Go and utterly destroy all that they have and do not spare them.”
Saul’s Actions
Saul gathered the people and numbered them. Then he camped against one of the Amalekite cities. He sent the Kenites living among the Amalekites away because they had befriended them on their journey. Then they attacked the Amalekites, took their king hostage, but destroyed the people. Saul and the people spared King Agag and the best of their livestock. Anything despised and worthless they destroyed.
Rejected
God spoke to Samuel. “I greatly regret that I have set up Saul as king.” He also told him why. “He has turned back from following Me and has not performed My commandments.” The situation grieved Samuel. All night long, he cried out to God. A God of justice and One who fulfills His promises, sent Samuel with instructions to Saul, who acted, but caused God to regret His choice.