From the state of mind it produces, the Fathers called it "opinion." Saint Gregory of Sinai and Saint John of Carpathos speak of it.
The holy Apostle Paul points to this kind of delusion when he says: "Let no one defraud you by a voluntary humility and worship of angels, intruding into those things which he has not seen, vainly puffed up by his fleshly mind" (Col 2:18).
The one possessed by this delusion imagines things about himself. He has formed an "opinion" about himself, that he possesses many virtues and merits, even that he abounds in gifts of the Holy Spirit.
Opinion is composed of false concepts and false sensations. By this property it belongs wholly to the realm of the father and representative of falsehood, the devil.
The man who prays tries to disclose in his heart the sensations of the new man. Since he has no possibility of doing this, he replaces them with sensations of his own invention, counterfeit sensations.
The action of fallen spirits is not slow to join these counterfeit sensations. Having accepted wrong sensations, both his own and demonic, as true and grace-filled, he receives concepts corresponding to those sensations.
These sensations are constantly assimilated by the heart and strengthened in it. They nourish and multiply false concepts.
It is natural that from such a wrong labor there arise self-delusion and demonic delusion, that is, "opinion."
"Opinion does not allow what is imagined to exist," said Saint Symeon the New Theologian.
One who imagines himself dispassionate will never be cleansed of the passions. One who imagines himself full of grace will never receive grace. One who imagines himself holy will never attain holiness.
Simply said, one who ascribes to himself spiritual works, virtues, merits, and gifts of grace flatters and amuses himself with "opinion."
By this "opinion" he bars the entrance into himself both to spiritual works, Christian virtues, and divine grace. He opens wide the entrance to sinful infection and to demons.
Those infected with "opinion" no longer have any capacity for spiritual progress. They have destroyed this capacity by offering on the altar of falsehood the very foundations of human activity and salvation, namely, concepts of truth.
An extraordinary pomposity appears in those sick with this delusion. They are as if drunk with themselves and with their state of self-delusion, seeing it as a state of grace.
They are saturated and filled with high-mindedness and pride. Yet they appear humble to many who judge by outward appearance.
Such people cannot evaluate by fruits, as the Savior commanded (Mt 7:16; Mt 12:33). Still less can they evaluate by the spiritual sense of which the Apostle speaks (Heb 5:14).
The Prophet Isaiah vividly depicted the action of the delusion of "opinion" in the fallen archangel. This action deceived and destroyed that archangel.
"You," the prophet says to Satan, "said in your mind: I will ascend into heaven. I will set my throne above the stars of heaven. I will sit on a high mountain, on the high mountains toward the north. I will ascend above the clouds. I will be like the Most High. But now you shall descend into Hades, to the foundations of the earth" (Is 14:13-15).
The Lord exposes the one infected with "opinion" in this way: "You say, I am rich, and have become wealthy, and have need of nothing. And you do not know that you are wretched, miserable, poor, blind, and naked."