David used his opportunity to defeat and to annihilate the common enemies of Israel and the Philistines that lived to Israel's southwest. David did not leave any survivors, as the Lord had commanded (Deut. 3:18-20; Josh. 1:13). He was clearing the Promised Land of foreign foes so the Israelites could occupy it. David walked a thin line of deception but was able to convince Achish that his victories were for the welfare of the Philistines and the detriment of Israel. Really he was conquering Israel's surrounding enemies, but he gave Achish the impression that his raids were against the southern portions in Judah. David continued to subdue Israel's enemy neighbors later when he became king (2 Sam. 8). Achish believed that David had alienated himself from the Israelites and would therefore be loyal to him from then on (v. 12; cf. 17:9).
"Like Nabal [in 25:10], Achish seriously underestimates David by regarding him as a servant or slave."271
