Abbot Haralambos Dionysiatis: Understand only the prayer

 As much as you can, my child, fall noetically with the fear of God, like the gypsy, at the feet of our Christ. And know this. You have come from the world. You are still carrying the world with you. The evil one will run through all the scenes of the world that you have inside you, all of them, like a tape in your mind. Continue to say the prayer. With perseverance, patience, and forcefulness. As much and you can, drive away whatever fantasy¹ is in your mind, whether it's good or bad. Compel yourself to understand only those five words of the prayer.

This is the first lesson, today. Let's see whether you have understood it.

+Abbot Haralambos Dionysiatis, from Abbot Haralambos Dionysiatis; The teacher of noetic prayer, Part 2, chapter A
¹ Fantasy is here understood as A mental image formed in the nous either by oneself or by the demons.

St. Mark the Ascetic: Enduring Sorrows which are the result of Sins

 If you wish to bring to God a blameless confession, then do not call to mind the images of previous sins, but courageously endure all the sorrows that come upon you as a result of these sins. Sorrows come as retribution for previous sins, the heaviness of each retribution depending on the heaviness of the sin. He who is wise and knows the truth confesses to God not by calling to mind his committed sins, but by enduring the sorrows that come as a result of those sins. If he rejects suffering and dishonor, he will not bring repentance even if he does other good deeds, for vanity and lack of suffering serve sin, even when the ascetic does good deeds.

+St. Mark the Ascetic, from On Those Who Think they are made Righteous by Works, in The Philokalia Volume 1, #193, 197,150-156

St. Ignatius Brianchaninov: On the Beginning of the Spiritual Life

 Brother! If you have not yet sensed the union of mind, soul, and body, then practice attentive prayer, uniting the prayer of the lips - sometimes spoken, sometimes whispered - with the mind. Act according to the commandments of the Gospel, battling the passions with endurance and long-suffering, never slipping into despair or hopelessness when you are defeated by sinful thoughts or emotions. At the same time, do not allow yourself to be defeated easily. Having fallen down, stand up. If you fall again, stand up again, until you learn how to walk without tripping. The cup of infirmity has its uses; until a proper time, the providence of God allows it, so that the ascetic can be purified of pride, anger, remembrance of evil, condemnation of others, arrogance, and vanity. It is especially important to recognize the action of vanity within yourself and to rein it in. While it acts in you, you will not be able to enter the domain of the spiritual life, for [the] price of entrance is a lack of passionate attachments, which is a gift received after the coming of the peace of Christ.

+St. Ignatius Brianchaninov, from The Refuge: Anchoring the Soul in God, Chapter 16 The Prayer of the Mind, the Heart, and the Soul.

St. Innocent of Alaska: The difficulty of Salvation

The way into the kingdom of heaven is difficult and there are bitter labors on it, but he who has not seen and experienced what is bitter cannot know the value of what is sweet. The way into the kingdom of heaven is difficult, but while suffering here on earth we can always pray and in prayer find comfort and strength, and God always hears our prayer. But when we die not as Christians, even if we could pray there, God would not hear us. The way into the kingdom of heaven is difficult, but the eternal sufferings and torments are incomparably greater and more grievous than earthly sufferings. Even our most grievous sufferings here below, in comparison with the sufferings of hell prepared for the devil and his angels, are so small that they are like tiny drops in comparison with the whole ocean. The way to heavenly beatitude is difficult, but are the ways to earthly fortune or happiness easier? Look how those labor and sweat who make money and seek earthly honor and glory, and how often we willingly and gladly undertake labors and cares for some empty pleasure. But what is the result? Instead of receiving pleasure we only lose time, waste money, ruin our health, and destroy our soul. Therefore, if we examine ourselves more attentively, it becomes clear that it is not because the way is difficult that we do not go into the heavenly kingdom but because we have no real desire or inclination to do so, and do not want to trouble ourselves about it. Whoever ardently desires anything will always seek it, in spite of all difficulties and obstacles. 

+St. Innocent of Alaska, from Indication of the Way into the Kingdom of Heaven