John Cassian, Conferences I–X VII.23: Of the diminished power of the devils

But we have thoroughly discovered both by our own experience and by the testimony of the Elders that the devils have not now the same power as they had formerly during the early days of the anchorites, when yet there were only a few monks living in the desert. For such was their fierceness that it was with difficulty that a few very steadfast men, and those advanced in years were able to endure a life of solitude. Since in the actual monasteries where eight or ten men used to live, their violence attacked them so and their assaults were experienced so frequently, and so visibly, that they did not dare all to go to bed at once by night, but took turns and while some snatched a little sleep, others kept watch and devoted themselves to Psalms and prayer and reading. And when the wants of nature compelled them to sleep, they awoke the others, and committed to them in like manner the duty of keeping watch over those who were going to bed. Whence we cannot doubt that one of two things has brought about this result not only in the case of us who seem to be fairly strong from the experience which our age gives us, but also in the case of younger men as well. For either the malice of the devils has been beaten back by the power of the cross penetrating even to the desert, and by its grace which shines everywhere; or else our carelessness makes them relax something of their first onslaught, as they scorn to attack us with the same energy with which they formerly raged against those most admirable soldiers of Christ; and by this deceit and ceasing from open attacks they do us still more damage. For we see that some have fallen into so sluggish a condition that they have to be coaxed by too gentle exhortations for fear lest they should forsake their cells and fall into more dangerous troubles, and wander and stray about and be entangled in what I would call grosser sins; and it is thought that a great thing is got from them if they can even with some listlessness remain in the desert, and the Elders often say to them as a great relief: Stop in your cells, and eat and drink and sleep as much as you like, if only you will stay in them always.