8 And David and his men went up and raided the Geshurites, the Girzites, and the Amalekites. For those nations were the inhabitants of the land from of old, as you go to Shur, even as far as the land of Egypt. 9 Whenever David attacked the land, he left neither man nor woman alive, but took away the sheep, the oxen, the donkeys, the camels, and the apparel, and returned and came to Achish. 10 Then Achish would say, "Where have you made a raid today?" And David would say, "Against the southern area of Judah, or against the southern area of the Jerahmeelites, or against the southern area of the Kenites." 11 David would save neither man nor woman alive, to bring news to Gath, saying, "Lest they should inform on us, saying, 'Thus David did.' " And thus was his behavior all the time he dwelt in the country of the Philistines. 12 So Achish believed David, saying, "He has made his people Israel utterly abhor him; therefore he will be my servant forever."
Matthew Henry's Commentary on 1 Samuel 27:8-12
Commentary on 1 Samuel 27:8-12
(Read 1 Samuel 27:8-12)
While David was in the land of the Philistines, he attacked some remains of the devoted nations. The people whom he cut off were long before doomed to destruction. It is often wisdom to shun public notice, but we must in no situation be idle. We must always try to do somewhat in the cause of God. This expedition David hid from Achish. But an equivocation which serves the purpose of a lie, is as like to it as a hypocrite is to a profane person, it is only better in appearance, therefore more dangerous. Yet, though believers often manifest imperfections, they can never be prevailed upon to renounce the service of God, and to unite interests with his enemies, or finally to become the servants of sin and Satan. But what a train of evils follow from unbelief! When we forget the Lord's past mercies, and his gracious assurances, we shall be overwhelmed with desponding fears, and probably be led to adopt some dishonourable method to get rid of our troubles. Nothing can so effectually establish us in holy tempers and practices, and preserve us from perplexities, as firm, unshaken dependence upon the promises of God in Christ Jesus.