The Works Of John Cassian by John Cassian
Chapter VIII. Of the fall and deception of a monk of Mesopotamia.
It is a long business too to tell the story of the deception of that monk of Mesopotamia, who observed an abstinence that could be imitated by but few in that country, which he had practised for many years concealed in his cell, and at last was so deceived by revelations and dreams that came from the devil that after so many labours and good deeds, in which he had surpassed all those who dwelt in the same parts, he actually relapsed miserably into Judaism and circumcision of the flesh. For when the devil by accustoming him to visions through the wish to entice him to believe a falsehood in the end, had like a messenger of truth revealed to him for a long while what was perfectly true, at length he showed him Christian folk together with the leaders of our religion and creed; viz. Apostles and Martyrs, in darkness and filth, and foul and disfigured with all squalor, and on the other hand the Jewish people with Moses, the patriarchs and prophets, dancing with all joy and shining with dazzling light; and so persuaded him that if he wanted to share their reward and bliss, he must at once submit to circumcision. And so none of these would have been so miserably deceived, if they had endeavoured to obtain a power of discretion. Thus the mischances and trials of many show how dangerous it is to be without the grace of discretion.