It seems to me that few people understand the extent of the cunning wickedness of these demons and the way in which they assist one another. I have known the demon of cowardice to fight and work together with that of listlessness. One comes to the aid of the other and reinforces him. The first brings fear and obduracy into the soul, the second produces darkness, negligence, blindness of heart and mind, and finally despair. Listlessness is a real trial for all those engaged in the spiritual struggle, but it becomes for them the ambassador of humility.
On that day God will not judge us about psalmody, nor for the neglect of prayer, but because by abandoning them, we have opened our door to the demons.
The demons, murderers as they are, push us into sin. Or if they fail to do this, they get us to pass judgment on those who are sinning, so that they may defile us with the stain which we ourselves are condemning in another.
Our enemies (demons) fell because of their pride, and call us to follow them, and bring us feelings of praise. And if your soul accepts that praise, then grace will depart, until the soul becomes humble again. And so all your life you must learn the humility of Christ.
If a man only theorises about God, then he is helpless, utterly helpless, when confronted by an evil spirit. An evil spirit laughs at feeble worldly theorising. But as soon as a man begins to fast and to pray to God, the evil spirit becomes filled with inexpressible fear.
St. John Climacus was asked if there are reliable signs by which it's possible to know whether a soul is drawing near to God or moving away from Him. After all, regarding ordinary things there are clear signs as to whether they're good or not. When, for instance, cabbage, meat or fish begins to rot, it's easy to notice it, since the rotting object begins to give off a foul odor, the color and taste change, and its external appearance witnesses to its deterioration. Well, and what about the soul? After all, it's bodiless and can't give off a bad smell or change its appearance. To this question the Holy Father replies, 'A sure sign of the deadening of the soul is the avoidance of church services.'
If anyone wants to drive out the demons, he must first subdue the passions, for he will banish the demon of the passion which he has mastered. For example, the devil accompanies anger; so it you control your anger, the devil of anger will be banished. And so it is with each of the passions.