There was nothing complicated about the command:
Kill all the Amalekites.
Apparently it was too complicated for Saul. He made good on warning the Kenites to get out of town to be spared complete destruction, destroyed most of the Amalekites, but spared the king, some livestock, and anything good he could benefit from.
God speaks to Samuel remorseful that he ever made Saul king. Samuel feels God’s grief and comes to Saul. Then things get sticky.
Here’s where Saul goes wrong:
1) He is boastful in his sin. He greets Samuel as though he done the right thing and rejoices in his victory.
2) He casts blame on his soldiers for the act, proving well that he knew what he had done was wrong. He doesn’t own up to his sin and places the fault on his people.
3) Even when confronted with Samuel’s straight forward accusation, Saul tries to justify his action by saying he has done exactly the right thing. “I did obey the voice of the LORD, and went on the [mission on which the LORD sent me, and have brought back Agag the king of Amalek.”
Bringing back Agag was not in the plan. I think Saul brought him back for bragging rights, as a trophy to say, “I had the opportunity to slay the king but in my power withheld.” Saul was on a power trip.
Then, Samuel lays the challenge:
Does the LORD delight in burnt offerings and sacrifices
as much as in obeying the LORD?
To obey is better than sacrifice,
and to heed is better than the fat of rams.
Saul finally confesses, owns up, and admits his fear. But there are still consequences.
The story isn’t finished, though. As Samuel leaves, Saul reaches for his cloak and tears it. Sam says:
The LORD has torn the kingdom of Israel from you today and has given it to one of your neighbors—to one better than you. He who is the Glory of Israel does not lie or change his mind; for he is not a human being, that he should change his mind.
The marvel of this story for me is that even in Saul’s sin, God leverages his disobedience to pull power out of his hands and give it to the line of David. The Lineage of Christ. Even though Saul blew it, God still made a way to cover up his error and the error of everyone to come after.