Bede

And Achish said, "Have you seen the man who is insane," etc.? David, indeed, suspected by the Gittites due to his reputation for virtues, industriously imitated the actions of one who was mad, so that he might be thought to be possessed and, pitied by those who saw him, released unharmed. But their king, unaware of his pretense, truly expelled him as if he were insane, excluding him from entering his house as a madman. Nor does the truth of allegory depart from the shadow of history. …

Commentary on Samuel ↗