oprelesti.ru is an educational website, dedicated to the concept of "delusion" or "prelest" in Orthodox theology: where does it originate from, why it is dangerous, how to discern and avoid it.
In Orthodoxy, prelest, spiritual delusion, spiritual deception, illusion (Greek word πλάνη - "plani", Russian прелесть -"prelest") is a dangerous consequence of action of the passions of pride and vainglory in a man. This is a carnal mindedness (Rom. 8:6), knowledge falsely so called (1 Tim. 6:20), false spiritual state, "the wounding of human nature by falsehood" (St. Ignatius (Brianchaninov)), a false view of oneself and one’s actions: prelest is man’s assimilation of a falsehood which he accepts as truth (St. Ignatius (Brianchaninov)). All human beings are in delusion, only in different degree of it, at least in the fact that they constantly sin and do not repent, not seeing the sins and believing themselves to be free from delusion. One of the highest degrees of prelest in the broadest sense is when someone does not see any sins in himself.
In the narrow sense, "prelest" in its ultimate form is when someone is very proud and sees oneself as holy, an elder, a person who attained spiritual success. St. Ambrose of Optina writes about this that "it is easier to turn every sinner to repentance than to bring a deluded person to reason". Sometimes in such condition people see false visions, i.e. demons appear in front of them in the form of Angels and tell something. Truly holy person being close to God and seeing the multitude of his sins never thinks about himself as holy and not only in the mind but in the feeling of the heart as well. Also, seeing their sins, saints confessed frequently, so if someone does not need Confession, he is already in delusion regardless of whether or not he sees visions.
One of the sections of the site is dedicated to another spiritual concept - concealment of sins in confession. At first sight, it is not connected to prelest. But in fact, sometimes concealment of sins is followed by delusion. Concealment of sins can be considered a kind of delusion itself i.e. a false view of oneself being based on a false belief: it is better to conceal a sin rather than to confess and receive forgiveness from the Lord. Concealment of sins and thoughts from the spiritual father is especially dangerous for the monastics. Holy Fathers say that only those thoughts should be confessed that are repeated and staying long in the mind. But if it is indeed such thought and it is concealed and remains unconfessed, the person can greatly harm himself. It can lead to delusion of visions and then it can even end in suicide. For example, elder Joseph the Hesychast used to speak about such cases with his disciples.
The purpose of this site is description of these spiritual phenomena mainly on the basis of the words of the Holy Fathers and the modern ascetics in order to give the reader an initial understanding of such phenomena. Of course, simple theoretical knowledge of information about these states is not a guarantee against falling into them. Also, even if someone had already fallen into delusion and was able with God's help to recover, that does not give enough experience not to fall again. For example, St. Silouan the Athonite was in delusion not once but twice. Nevertheless, even such theoretical knowledge about delusion can sometimes help to see it for oneself when it is still weak. In particular, such situation is described in one of the articles where an ordinary man, not even a monk, realized the fact of demonic attacks recalling what he had read about it and addressed to a priest for help.