1 Samuel 27:8 - Joseph Benson’s Commentary on the Old and New Testaments

David and his men invaded the Geshurites, &c. These were some remains of the Amorites, and other ancient inhabitants of the country; whom God, for their inveterate and incorrigible wickedness, had commanded to be extirpated. And they “were not confederate with Achish, but in a state of hostility with him; particularly the Amalekites, whom we find soon after making great depredations upon the Philistine territories, chap. 1 Samuel 30:16. David, therefore, did not act in the least dishonourably by him, but in reality for his service, in the attack he made on them. It is further to be remarked, that as those people were on the south of Judah, they made frequent incursions into the land, and were the avowed enemies of the Hebrews. This is certain at least of the Amalekites, the remnant of those whom Saul destroyed, (chap. 15.,) who had retired into remote and distant places. Of these frequent mention is made in the books of the Old Testament, as engaged in many expeditions to plunder the country and destroy the inhabitants. David, therefore, had a right to cut off those nations; as deserving the character of a man after God's own heart, he was called upon to do it; and in doing it he served his country, without injuring his protector and friend.” Chandler. But it has been objected, that it was unjustifiable in David, being a private man, to act thus without a warrant from Achish or from God, which it does not appear that he had. In answer to this it must be observed, that he did not act as a private man, but as one elected and anointed to the kingdom. And “the same Spirit of God which once inspired Saul with all regal virtues, was now gone over to David, and rested on him, and it were very strange if David, as king-elect of Israel, could have any guilt in doing that which Saul, as a king in possession, was deposed for not doing.” Delaney.