David had no guarantee that he would receive asylum from Achish. It was a risky move.1 Nevertheless, from Achish’s perspective, given the troops that David brought with him, he would have a strong mercenary force to make use of if he allowed David to stay with him. David’s reputation as an outcast and enemy of Saul would also have been more well known than before (see 1 Samuel 21:10–15).2 If your enemy’s enemy is your friend, then one can understand why the enemy of Saul (Achish) would have given refuge to another enemy of Saul (David).
3 And David lived with Achish at Gath, he and his men, every man with his household, and David with his two wives, Ahinoam of Jezreel, and Abigail of Carmel, Nabal’s widow.