It is certainly impossible that King David would have been willing, as this verse implies, to wage war against Israel. Though he was fleeing from King Shaul (Saul), David remains completely loyal to his people throughout his travails. In this instance, he feigns loyalty to Achish and uses the advantage gained by his trust to spy against the Philistines, gaining information which will later helps him defeat this enemy. This is reminiscent of a more recent Israeli spy, Eli Cohen. During the 1960’s Cohen managed to infiltrate the highest echelons of the Syrian army, to spy on Israel’s behalf. He provided the I.D.F. with critical information that would assist Israel in the Six Day War and enable it to liberate the Golan Heights. Though Cohen was captured and executed by the Syrians, the State and People of Israel continue to benefit from his sacrifice to this very day. The Golan Heights is home to flourishing communities, and provides great strategic value to Israel.
Source: Israel in the News