Insanity, he was quite sure, was caused by Satan, and he exorcised sufferers.

Against some he appears to have advised stronger remedies; and his horror of idiocy, as resulting from Satanic influence, was so great, that on one occasion he appears to have advised the killing of an idiot child, as being the direct offspring of Satan.

Yet Luther was one of the most tender and loving of men; in the whole range of literature there is hardly anything more touching than his words and tributes to children.

In enforcing his ideas regarding insanity, he laid stress especially upon the question of St.Paul as to the bewitching of the Galatians, and, regarding idiocy, on the account in Genesis of the birth of children whose fathers were "sons of God" and whose mothers were "daughters of men." One idea of his was especially characteristic.
The descent of Christ into hell was a frequent topic of discussion in the Reformed Church.

Melanchthon, with his love of Greek studies, held that the purpose of the Saviour in making such a descent was to make himself known to the great and noble men of antiquity--Plato, Socrates, and the rest; but Luther insisted that his purpose was to conquer Satan in a hand-to-hand struggle.
This idea of diabolic influence pervaded his conversation, his preaching, his writings, and spread thence to the Lutheran Church in general.