Therefore they have often driven many to despair and hopelessness, destroying all hope, like the worm in the tree.
Often during the Divine Liturgy, and in the most terrible hour of the Sacraments, these vile thoughts blaspheme the Lord and the holy sacrifice being made. Hence it is evident that it is not our soul that utters these unholy, incomprehensible and inexplicable words within us, but a demon who hates God, who has been cast down from heaven because he attempted to blaspheme God there as well. And if these are my dishonorable and absurd utterances, how can I, having accepted this heavenly gift, worship? How can I bless and at the same time malign?
Often this deceiver and murderer has driven many into a mental frenzy. No thought is as difficult to confess as this one and therefore it lingers in many until old age. Nothing strengthens us against demons and evil thoughts so much as the fact that we do not confess them, but we hide them and feed them in our hearts.
No one should think that he is guilty of evil thoughts; for the Lord is a heart-watcher, and knows that such words are not ours, but our enemies'.
Drunkenness is the cause of stumbling, and pride is the cause of evil thoughts. Though he who stumbles is not guilty for stumbling, he will surely be punished for drunkenness.
When we stand in prayer, these unclean and inexpressible thoughts rise up against us, but at the end of prayer they immediately depart from us; for they are not in the habit of contending with those who do not arm themselves against them.
This godless spirit not only blasphemes against God and all divine things, but also speaks shameful and dishonorable words in us, so that we either forsake prayer or fall into despair.
This wicked and dishonorable tormentor has led many away from prayer, excommunicated many from the Holy Mysteries, weary some of their bodies with sorrow, and weary some with fasting, without giving them the slightest sign of relief.
He does this not only to the laity, but also to those who are going through monastic life, telling them that there is no hope of salvation for them and that they are more repentant than all infidels and pagans.
Whom the spirit of blasphemy troubles, and who wishes to get rid of it, let him surely know, that not his soul is guilty of such thoughts, but of an unclean demon, who once said to the Lord himself: I will give all this to you, but if you worship me (Matt.4:9). Therefore, we also, despising him, and counting his imputed thoughts for nothing, say to him: go after me, Satan: to the Lord my God I will worship, and to Him alone I will obey; but thy disease and thy words shall be turned upon thy head, and upon thy top thy blasphemy shall fall in the present age and in the future (Psalm 7:17).
Whoever would otherwise want to defeat the demon of blasphemy would be like the one who tries to hold back the lightning with his hands. For how is it possible to catch, contend, and fight with one who suddenly, like the wind, flies into the heart, instantly utters a word, and immediately disappears? All the other enemies, standing, struggling, slowing down and giving time to those who move against them. This is not the case: he had just appeared and already retreated, he spoke - and disappeared.
This devil often tries to attack the simplest of mind and not evil, which more than others worried and disturbed by this, but about them can be said fairly, that all this happens to them not from their vauntedness, but the envy of demons.
Let us cease from judging and condemning our neighbor, and we shall not be afraid of blasphemous thoughts; for the cause and root of the latter is the former.
As one who is shut up in a house hears the words of passers-by, though he himself does not speak to them: so the soul, abiding in itself, hearing the devil's blasphemies, is embarrassed by what he, passing by, utters.
He that despiseth this foe shall be delivered from his torment; but he that striveth otherwise to wage war against him, by him he shall prevail. He who seeks to overcome the spirits with words is like one who seeks to shut out the winds.
One monk, suffering attacks from this demon for twenty years, exhausting his body fasting and vigil, but as one who received no benefit from this, then, describing on a paper this his temptation, went to a certain holy man and giving him it, his face turned to the ground, not daring to look at him. The elder, after reading what was written, smiled, and lifting the brother up, said to him, "Put your hand on my neck, child." When he did this, the great man said to him, "On my neck, brother, let this sin be, no matter how many years it has lasted and will continue in you; only you can count it as nothing." Afterwards the monk assured me that before he had even left the monk's cell, the passion had disappeared. This he himself, who had been tempted, told me, giving thanks to God.
"The Ladder or Tablets of the Spirit" by St. John the Abbot of Mount Sinai, Word 23
Source: 3rm.info (Russian)