Charles Ellicott Commentary 1 Samuel 21:14

"Then said Achish unto his servants, Lo, ye see the man is mad; wherefore then have ye brought him to me?" — 1 Samuel 21:14 (ASV)

Then said Achish ... the man is mad. —The Philistine king would look with particular sorrow and repulsion on a madman if, according to Jewish tradition (see Philippson), his own wife and daughter were insane.

The device, however, succeeded, as David hoped it would, and he was allowed to depart in safety—indeed, he was even hurried out of the Philistine country. In ancient times, as is still the case today in many parts of the East, insane people are regarded as individuals in some special way touched by, and therefore under the more immediate protection of, the divine. The life of the hunted fugitive was then perfectly safe from the moment the Philistines considered him mad.

There is a curious legend in the Talmud in which several events recorded in the Biblical account are confused. Part of it apparently refers to his strange choice of Philistia as a place of refuge. “One day Satan appeared to him (David) in the shape of a gazelle, which, eluding his pursuit, decoyed him into the land of the Philistines. ‘Ah!’ said Ishbi-benob, when he caught sight of him, ‘are you the man who killed my brother, Goliath?’ So saying, he seized and bound him.”—Treatise Sanhedrin, folio 95, Colossians 1:2. The wild legend goes on to explain how, partly by miracle and partly with the aid of Abishai, David killed Ishbi-benob and escaped.