"Somewhere in the desert at the back of Alexandria there was once a monastery whose abbot possessed the power of clairvoyance. Among his monks there were two young men who had an especial reputation for purity and holiness... One day when they were singing in the choir it occurred to the abbot to turn his clairvoyant faculty upon these two young men... he looked at the first young man and saw that he had surrounded himself with a shell as of glittering crystal, and that when the tempting demons (impure thought-forms we should call them) came rushing at him, they struck against this shell, and fell back without injuring him, so that he remained inside his shell, calm and cold and pure. Then the abbot looked at the second young monk, and he saw that he had built no shell round himself, but that his heart was so full of the love of God that it was perpetually radiating- from him in all directions in the shape of torrents of love for his fellowmen, so that when the attempting- demons sprang at him with foul intent they were all washed away in that mighty outpouring stream, and so he also remained pure and undefiled... p. 477"