The source of spiritual delusion, like any other evil, is the devil, not some kind of virtue. The beginning of delusion is pride, and its fruit is overwhelming pride.
A dreamer, from the first step on the path of prayer, moves away from the realm of truth into the realm of lies, into the realm of Satan, and subjects himself deliberately to the influence of Satan. All Holy Fathers, who described the feat of mindful prayer, do not only prohibit any arbitrary dreams, but also being inclined to dreams and apparitions with unrestrained imagination and desire, in which case they may appear to us unexpectedly, no matter what we do.
Saint Ignatius (Bryanchaninov)
Woe to the soul, which does not feel its sores and thinks that it is completely beyond the damage of evil, for it is precisely because of the great, immeasurable damage of evil that it feels so. The good Physician no longer visits such a soul nor treats it, for it has neglected to take care of its sores arbitrarily, and thinks of itself as though it were healthy and impeccable. “They that are whole have no need of the physician, but they that are sick,” says the Lord.
Saint Macarius of Egypt
Would you like to know what delusion is: delusions have a variety of effects, as the mind and heart become prouder, they are darkened and captivated by self-conceit and self-centeredness, and the very intellect believes in the opinions and dreams which are presented to it by the universal enemy – the devil, and thus becomes frenetic and utters the absurdities it perceives due to its opinions and dreams, and this means being deluded.
Saint Leo of Optina
It is fitting to know that there are three main reasons for spiritual delusion: pride, the jealousy of demons, and a punishment. Those three causes have the following reasons: pride is caused by vain carelessness (or vanity), jealousy is caused by success, and punishment is caused by a sinful life. The delusion caused by jealousy or pride is more likely to be healed, especially if one humbles himself. However, the delusion that comes as a punishment – when one is given up to Satan for sins – is often permitted by God through His abandonment to the point of death. It happens that even the innocent are tormented by demons for the sake of salvation. It is fitting to know that the spirit of proud conceit also gives prophecies sometimes to those who do not pay careful attention to their hearts.
Saint Gregory of Sinai
The wise Solomon says in the Proverbs, “Where no counsel is, the people fall: but in the multitude of counselors there is safety” (Proverbs 11:14). Dear brothers, can you see how powerful this saying is? Can you see what the Holy Scripture teaches us? It exhorts us not to rely on ourselves, not to consider ourselves reasonable, not to believe that we can manage ourselves, because we need help, we need those who guide us to God.
Holy Abba Dorotheus
You want to see that you live well and are getting saved, but you do not realize that this brings about spiritual delusion, whereas our infirmities make us humble.
Saint Macarius of Optina
The onset of mental darkness (when its symptoms begin to unfold in the soul) is primarily found in becoming lazy to serve God and to pray. For if the soul does not fall away from these first, there is no other way for spiritual seduction; but when it loses God’s help, it easily falls into the hands of its adversaries. Moreover, as soon as the soul becomes reckless with regard to virtues, it is inevitably carried away in things that are opposed to them. For the transition from any side is already the beginning of the opposite side. Virtue means taking care of the soul, and not of the mundane matters. Reveal your weakness before God incessantly, and you will not be tempted by aliens, as soon as you are alone without your Protector.
Saint Isaac the Syrian
Demons make three pitfalls for us whenever we try to please God. First, they fight to prevent us from doing good. Secondly, when they are defeated in this first attempt, they try to make sure that what we have done is not according to God’s will. If they fail to succeed in this intention, then they quietly come to our soul and pamper us as though we were living in harmony with everything that God wants. The first temptation is resisted by the carefulness and care of death; the second by obedience and humiliation; and the third by the constant self-abasement. This work is before us, until we go into the sanctuary of God (cf. Psalm 73:17). Then we shall no longer suffer the violence of evil habits; for our God is a consuming fire (Hebrews 12:29) and He consumes every burning and movement of lust, every bad habit, every bitterness and wickedness, both inner and outer, visible and conceivable.
Saint John of the Ladder
The Novice Eustolia, the woman of prayer, is afraid to fall into delusion. – May she hold fast to Godly humility, considering herself in the innermost heart to be the most sinful of all humans, and then she will not fall into delusion. For as the Holy Fathers remarked, “humility cannot fall.”
Saint Joseph of Optina
Translated by The Catalogue of Good Deeds