Rabanus Maurus
Catena Aurea · Matthäusevangelium 17
And when they were come to the multitude, there came to him a certain man, kneeling down to him, and saying, Lord, have mercy on my son: for he is lunatick, and sore vexed: for ofttimes he falleth into the fire, and oft into the water. And I brought him to thy disciples, and they could not cure him. Then Jesus answered and said, O faithless and perverse generation, how long shall I be with you? how long shall I suffer you? bring him hither to me. And Jesus rebuked the devil; and he departed out of him: and the child was cured from that very hour.
The lunatic is figuratively one who is hurried into fresh vices every hour, one while is cast into the fire, with which the hearts of the adulterers burn; or again into the waters of pleasures or lusts, which yet have not strength to quench love. (Hos. 7:4, 6.)