2 Thus says the Lord of hosts, "I will punish the Amalekites for what they did in opposing the Israelites when they came up out of Egypt.

Matthew Henry's Commentary on 1 Samuel 15:2

Commentary on 1 Samuel 15:1-9

(Read 1 Samuel 15:1-9)

The sentence of condemnation against the Amalekites had gone forth long before, Revelation 18:4. As the commandment had been express, and a test of Saul's obedience, his conduct evidently was the effect of a proud, rebellious spirit. He destroyed only the refuse, that was good for little. That which was now destroyed was sacrificed to the justice of God.