Saint Nicolai Velimirovich. "The Prologue."
The spiritists of our time accept every appearance from the spiritual world as sent by God and immediately boast that it has been 'revealed' to them. I was myself acquainted with an eighty-year-old monk who was respected by everyone as a great spiritual guide. When I asked him if he had ever seen any being from the spiritual world in his lifetime, he answered me: 'No, never; and praise be to God for his mercy!' Seeing my astonishment at this, he said: 'I have constantly prayed to God that nothing should ever appear to me, lest I fall into illusion and accept a devil disguised as an angel. And, until now, God has heard my prayer.