Charles Ellicott Commentary Matthew 17:15

"Lord, have mercy on my son: for he is epileptic, and suffereth grievously; for oft-times he falleth into the fire, and off-times into the water." — Matthew 17:15 (ASV)

Lunatick—See the note on Matthew 4:24.

The other Gospels add further details. The boy had a dumb spirit. When the spirit seized him, it tore him, and he foamed at the mouth and gnashed his teeth. The seizure passed slowly and with difficulty, and the sufferer was wasting away from the violence of the attacks.

It should be noted that the phenomena described are those of epilepsy complicated with insanity. This is a combination common in all countries and was likely aggravated in a culture where the "seizure"—which the very word epilepsy implies—was believed to be the work of a supernatural power. Medical writers note all these symptoms: prolonged melancholy, an indescribable look of sadness, a sudden fall and loss of consciousness (with or without convulsions, or passing into a tetanic stiffness), and a periodic recurrence that often coincides with the new or full moon. This recurrence is likely the reason the boy was described as a "lunatic." Grinding the teeth and foaming at the mouth are also classic symptoms.

In the early stages of medical science, the names for this condition all indicated the awe with which people viewed it. It was called the "divine" or "sacred" disease, seen as a direct supernatural affliction. The Latin synonym, morbus comitialis, arose because if such a seizure occurred during the comitia, or assemblies of the Roman Republic, it was considered such an evil omen that the meeting was immediately broken up and all business was adjourned.

Whether this case involved something more than disease—namely, a distinct possession by a supernatural force—is a question that belongs to the general subject of the "demoniacs" in the Gospel records (see the note on Matthew 8:28). Here, at any rate, our Lord’s words in Matthew 17:21 assume the reality of the possession even more emphatically than elsewhere .