For he is lunatic: not a mad man, but troubled with the epileptic disease; upon which, as on madness or lunacy, the changes and full of the moon have an influence: hence the next clause,
and sore vexed, is rendered in the Arabic version, "and sore vexed at the beginning of full moons"; at which times, he had very grievous and frequent fits of his disorder:
for ofttimes he falleth into the fire, and oft into the water: which shows it to be the "epilepsy", or "falling sickness", he was afflicted with; which, whenever it seized him, whether by the fireside, or by the side of a river or brook, or any place of water, or in any other dangerous situation, he fell into it, not being able to help himself, or avoid any danger to which he was exposed. A larger account of this child's disorder, and of the circumstances of his cure, are related by Mark 9:17 where this case will be more fully considered. See Gill on Mark 9:17. See Gill on Mark 9:18.