Saint John Climacus. "The Ladder of Divine Ascent". Step 26.
When we begin religious life, some unclean demons give us lessons in the interpretation of scripture. This happens particularly in the case of people who are either vainglorious or who have had a secular education, and these are gradually led into heresy and blasphemy. One may detect this diabolical teaching about God, or rather war against God, by the upheaval, confusion, and unholy joy in the soul during lessons.