David arose, and fled that day for fear of Saul, and went to Achish the king of Gath.
"Shall this fellow come into my house"  (1 Samuel 21:15).  "These words are an idiom meaning, `To be allowed to dwell in one's city or country.'"[20]  This clarifies the whole episode.  David intended to ask Achish for permission to dwell in Gath, probably having good reason to suppose that Achish would have honored his request.  However, the soldiers of Achish recognized David, arrested him and would most certainly have opposed any inclination of Achish to grant political asylum to David.  This severely frightened David, and he immediately began feigning madness. This, of course gave him the opportunity to escape and keep the rendezvous with his men.