What does 1 Samuel 15:19 mean?

Samuel has affirmed that God anointed Saul over Israel and gave him a specific mission to fully eliminate the depraved nation of the Amalekites (1 Samuel 15:17–18). Saul's authority from the Lord and the assigned task were clear. Now, Samuel asks why Saul felt he could reject something the Lord commanded him?

Samuel's second question puts a fine point in Saul's disobedience: you kept the most valuable and interesting spoils of war. It was the typical right of armies to take the belongings of the enemies they conquered in battle. Saul and his men had fought many battles with Israel's enemies (1 Samuel 14:47). Gathering the valuables of beaten foes was one of the benefits of taking on the risks of combat. But this campaign was supposed to be different. In this battle, the Israelites were acting as God's instrument of judgment on the Amalekites (Exodus 17:14–16; Deuteronomy 25:17–19). Everything was to be "devoted to destruction" (1 Samuel 15:2–3); no spoils were to remain and nothing was to be taken. Nothing connected to the wicked Amalekite culture was to be preserved.

Saul's refusal to obey the direct command of the Lord, instead treating this as any other battle and taking plunder, was evil in God's sight. Saul's motive for disobedience is unclear. It might have been out of greed for the riches of the livestock or out of fear of his own soldiers who wanted to keep the animals for themselves. Whatever the reason, Samuel is clear: Saul did evil in God's sight by not fully obeying God's command.