The Devil chooses to deceive some people in the following way. He will marvelously inflame their brains with the desire to uphold God’s law and destroy sin in everyone else. He will never tempt them with anything that is manifestly evil. He makes them like anxious prelates watching over the lives of Christian people of all ranks, as an abbot does over his monks. They will rebuke everyone for their faults, just as if they had their souls in their care; and it seems to them that they dare not do otherwise for God’s sake. They tell them of the faults they see, claiming to be impelled to do so by the fire of charity and the love of God in their hearts; but in truth they are lying, for it is by the fire of hell surging in their brains and their imaginations.
— The Cloud of Unknowing (14th century), Chapter 55