Bede the Venerable — as excerpted in the Catena Aurea on Mark 9:14-29

“(ubi sup.) Or by this demoniac are signified those, who are bound by the guilt of original sin, and coming into the world as criminals, are to be saved by grace; and by fire is meant the heat of anger, by water, the pleasures of the flesh, which melt the soul by their sweetness. But He did not rebuke the boy, who suffered violence, but the devil, who inflicted it, because he who desires to amend a sinner, ought, whilst he exterminates his vice by rebuking and cursing it, to love and cherish the man.”