And he took Agag the king of the Amalekites alive, and utterly destroyed all the people with the edge of the sword.

Wesley's Notes

15:8 All - Whom he found. Now they paid dear for the sin of their ancestors. They were themselves guilty of idolatry and numberless sins, for which they deserved to be cut off. Yet when God would reckon with them, he fixes upon this as the ground of his quarrel.

Jamieson-Fausset-Brown Bible Commentary

8, 9. he took Agag . alive-This was the common title of the Amalekite kings. He had no scruple about the apparent cruelty of it, for he made fierce and indiscriminate havoc of the people. But he spared Agag, probably to enjoy the glory of displaying so distinguished a captive, and, in like manner, the most valuable portions of the booty, as the cattle. By this wilful and partial obedience to a positive command [1Sa 15:3], complying with it in some parts and violating it in others, as suited his own taste and humor, Saul showed his selfish, arbitrary temper, and his love of despotic power, and his utter unfitness to perform the duties of a delegated king in Israel.

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.