Achish said, Surely, as the Lord liveth He swears by Jehovah, whom David worshipped, that he might be the more believed by him. Or perhaps he had learned something from David of the true God, though he worshipped other gods with him.
Related Commentaries of 1 Samuel 29:6
1 Samuel 29:6
6 Then Achish called David, and said unto him, Surely, as the LORD liveth, thou hast been upright, and thy going out and thy coming in with me in the host is good in my sight: for I have not found evil in thee since the day of thy coming unto me unto this day: nevertheless the lordsa favour thee not.