Thus saith the LORD of hosts, I remember that which Amalek did to Israel, how he laid wait for him in the way, when he came up from Egypt.

Wesley's Notes

15:2 I remember - Now I will revenge those old injuries of the Amalekites on their children: who continue in their parents practices. Came from Egypt - When he was newly come out of cruel and long bondage, and was now weak, and weary, and faint, and hungry, Deut 25:18, and therefore it was barbarous instead of that pity which even Nature prompted them to afford, to add affliction to the afflicted; it was also horrid impiety to fight against God himself and to lift up their hand in a manner against the Lord's throne, whilst they struck at that people which God had brought forth in so stupendous a way.

Jamieson-Fausset-Brown Bible Commentary

2, 3. Amalek-the powerful tribe which inhabited the country immediately to the eastward of the northern Cushites. Their territory extended over the whole of the eastern portion of the desert of Sinai to Rephidim-the earliest opponent (De 25:18; Ex 17:8-16)-the hereditary and restless enemy of Israel (Nu 14:45; Jud 3:13; 6:3), and who had not repented (1Sa 14:48) of their bitter and sleepless hatred during the five hundred years that had elapsed since their doom was pronounced. Being a people of nomadic habits, they were as plundering and dangerous as the Bedouin Arabs, particularly to the southern tribes. The national interest required, and God, as King of Israel, decreed that this public enemy should be removed. Their destruction was to be without reservation or exception.

I remember-I am reminded of what Amalek did-perhaps by the still remaining trophy or memorial erected by Moses (Ex 17:15, 16).

Matthew Henry's Concise Commentary

15:1-9 The sentence of condemnation against the Amalekites had gone forth long before, Ex 17:14; De 25:19, but they had been spared till they filled up the measure of their sins. We are sure that the righteous Lord does no injustice to any. The remembering the kindness of the ancestors of the Kenites, in favour to them, at the time God was punishing the injuries done by the ancestors of the Amalekites, tended to clear the righteousness of God in this dispensation. It is dangerous to be found in the company of God's enemies, and it is our duty and interest to come out from among them, lest we share in their sins and plagues, Re 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.