Spiritual Deception - Prelest

Saint Theophan the Recluse
The more advanced a man is in holiness, the deeper is his awareness of his own sinfulness. Conversely, the less refined a man is, the weaker is his awareness of his own sinfulness. In the majority of people Such an awareness is altogether absent. This is why they do not understand the ascetic labor of repentance and do not feel any need for it. Because they do not understand this labor and feel no need to repent, one may say that all such people are in prelest. And inasmuch as we have but a limited awareness of our sinfulness, one may say that we are all in prelest !

Abba Poemen the Great:
"I prefer a man who sins and repents to one who does not sin and does not repent. The first has good thoughts, for he admits that he is sinful. But the second has false, soul-destroying thoughts, for he imagines himself to be righteous"

St. Isaac the Syrian wrote about this kind of prelest:
"The effect of the cross is twofold; the duality of its nature divides it into two parts, One consists in enduring sorrows of the flesh which are brought about by the action of the excitable part of the soul, and this part is called activity. The other part lies in the finer workings of the mind and in divine meditation, as well as in attending to prayer, etc.; it is accomplished by means of the desiring part of the soul and is called contemplation. The part of the soul by dint of its zeal, while the second part is the activity of soulful love, in other words, natural desire, which enlightens the rational part of the soul. Every man who, before perfectly mastering the first part, switches to the second, attracted out of weakness--to say nothing of laziness, is overtaken by God's wrath because he did not first mortify his members which are upon the earth (Col. 3:5). In other words, he did not cure his thoughts of infirmities by patiently bearing the cross, but rather dared in his mind to envision the glory of the cross"