John Lightfoot on Matthew 17:15

[He is lunatic.] Luke 9:39, a spirit taketh him; Mark 9:17, hath a dumb spirit.

I. He that is skilled in the Talmudic writings will here remember what things are said concerning a deaf and mad man, concerning whom there is so much mention in their writings.

"There are five who do not pay the Trumah; but if they do, their Trumah is no Trumah: the deaf and dumb, the lunatic," &c. "Any one is fit to sacrifice a beast, except a dumb and deaf, a lunatic, and a child": and very many passages of this nature, &c. I have rendered deaf and dumb, according to the sense of the masters, who, in the first place cited, do thus interpret the word; "concerning which the wise men speak, is he who neither heareth nor speaketh." See there the Jerusalem Gemara, where, among other things, this occurs not unworthy our noting; "That all the sons of R. Jochanan Ben Gudgoda were deaf and dumb."

II. It was very usual to the Jews to attribute some of the more grievous diseases to evil spirits, specially those wherein either the body was distorted, or the mind disturbed and tossed with a phrensy.

"If any one, vexed with an evil spirit, shall say, when the disease did first invade him, Write a bill of divorce for my wife," &c.

"If any, whom Kordicus vexeth, say, Write a bill of divorce for my wife," &c. "Kordicus, say the Glossers, is a demon, which rules over those that drink too much new wine. What is 'Kordicus?' Samuel saith, When new wine out of the press hath caught any one." Rambam, upon the place, hath these words; "Kordicus is a disease, generated from the repletion of the vessels of the brain, whereby the understanding is confounded; and it is a kind of falling-sickness." Behold the same a demon and a disease! to which the Gemarists applied exorcisms and a diet.

"Shibta is an evil spirit, who, taking hold on the necks of infants, dries up and contracts their nerves."

"He that drinks up double cups, is punished by the devils."

From this vulgar opinion of the nation, namely, that devils are the authors of such kind of diseases, one evangelist brings in the father of this child, saying of him he is lunatic, another, he hath a spirit. He had been dumb and deaf from his birth; to that misery was added a phrensy, or a lycanthropy, which kind of disease it was not unusual with the nation to attribute to the devil; and here, in truth, a devil was present.