David said in his heart, I shall now perish one day by the hand of Saul: there is nothing better for me than that I should escape into the land of the Philistines; and Saul will despair of me, to seek me any more in all the borders of Israel: so shall I escape out of his hand.
Why would David have been welcome in Philistia? Probably Achish and the other Philistine lords rejoiced to see the rift that existed between David and Saul.