The reason that fasting has an effect on the spirits of evil rests in its powerful effect on our own spirit. A body subdued by fasting brings the human spirit freedom, strength, sobriety, purity, and keen discernment.
A man may seem to be silent, but if his heart is condemning others, he is babbling ceaselessly. But there may be another who talks from morning till night and yet he is truly silent, that is, he says nothing that is not profitable.
Having guarded ourselves against distractions and worries, let us turn our attention to our body on which mental vigilance is completely dependent. Human bodies differ widely from one another in strength and health. Some by their strength are like copper and iron; others are frail like grass. For this reason everyone should rule his body with great prudence, after exploring his physical powers. For a strong and healthy body, special fasts and vigils are suitable; they make it lighter, and give the mind a special wakefulness. A weak body should be strengthened by food and sleep according to one's physical needs, but on no account to satiety. Satiety is extremely harmful even for a weak body; it weakens it, and makes it susceptible to disease. Wise temperance of the stomach is a door to all the virtues. Restrain the stomach, and you will enter Paradise. But if you please and pamper your stomach, you will hurl yourself over the precipice of bodily impurity, into the fire of wrath and fury, you will coarsen and darken your mind, and in this way you will ruin your powers of attention and self-control, your sobriety and vigilance…
Self-accusation before God is something that is very necessary for us; and humility of heart is extremely advantageous in our lives, above all at the time of prayer. For prayer requires great attention and needs a proper awareness, otherwise it will turn out to be unacceptable and rejected, and `it will be turned back empty' to our bosom.
We came from Palestine to Egypt and went to see one of the fathers. He offered us hospitality and we said, 'Why do you not keep the fast when visitors come to see you? In Palestine they keep it.' He replied, 'Fasting is always with me but I cannot always have you here. It is useful and necessary to fast, but we choose whether we will fast or not. What God commands is perfect love. I receive Christ in you and so I must do everything possible to serve you with love. When I have sent you on your way, then I can continue my rule of fasting. The sons of the bridegroom cannot fast while the bridegroom is with them; when he is taken away from them, then they will fast.'
The practice of the prayer of Jesus holy David, or more accurately the Holy Spirit by the mouth of David, offers to all Christians without exception: 'The kings of the earth and all people, princes and all judges of the earth, young men and maidens - let elders with the young praise the name of the Lord, for His name alone is exalted (PS. 148:11-13).' A literal understanding of the states enumerated here would be perfectly permissible, but their essential meaning is spiritual.
As the earth, long awaiting moistening and at last receiving it in abundance, suddenly is covered by tender and bright greenery, so also the heart, exhausted by dryness, and afterwards revived by tears, emits from itself a multitude of spiritual thoughts and feelings, adorned by the common flower of humility. The labor of weeping, being inseparable from the labor of prayer, requires the same conditions for success as prayer requires. Prayer needs patient, constant dwelling in itself; weeping requires the same. Prayer needs wearying of the body, and brings about exhaustion of the body; this exhaustion produces weeping, which must be born in the troubling and wearying of the body.
In order to remain in vigilance, it is necessary to guard the freshness and brightness of the mind with all care. The mind becomes darkened from imprudent use of food, drink and sleep, from much talking, from distraction and from worldly cares. Attend to yourselves, said the Lord, be on your guard and take care that your hearts are never weighed down, dulled and depressed by self-indulgence, overeating and drinking, or worldly cares and pleasures, lest that day (the day of Christ's dread judgment, the last day of the world) catch you unawares. For it will spring like a trap upon all who are living on the face of the earth. So watch and pray at all times for the strength to escape or survive all that is going to happen, and to stand before the Son of Man.
When Abba Agathon went down to the city to sell some of his baskets and to procure a little bread, he found near the market place an old, poor cripple. 'For the love of God, Abba,' the cripple began to plead on seeing the Saint, 'don't you, too, leave this poor wretch unaided. Bring me near to you.' Abba Agathon picked the man up and sat him next to him in the place where he had set up his baskets to sell them. 'How much money did you make, Abba?' the cripple would ask each time that the Elder sold a basket. 'Such and such,' the Elder would tell him. 'That's good enough,' the cripple finally said. 'Won't you buy me a little pie, Abba? That would be good of you, since I have not eaten since last evening.' 'With pleasure,' the Saint told him, immediately fulfilling the cripple's request. Shortly thereafter, the cripple requested some fruit. And then some sweet. Thus, for each basket that was sold, the Saint spent the proceeds, until, thanks to his patronage, all of the baskets and money were gone, without his having kept even two pennies for himself. More importantly, he did this all with great eagerness, even though he knew that he would thus go perhaps two weeks without any bread for himself. Since he had sold his last basket, the Saint got ready to leave the marketplace. 'So you're going?' the cripple asked him. 'Yes, I have completed all of my work.' 'Uh, do me the favor of taking me as far as the crossroads, and you can leave for the desert from there,' the strange old man again pleadingly said. The good Agathon took the cripple on his back and carried him to the place where he wanted to go, though with great difficulty, since he was exhausted from his day's work. As soon as he reached the crossroads and started to put down his living burden, he heard a sweet voice say to him: 'May you be blessed, Agathon, by God, both on earth and in Heaven.' The Saint raised up his eyes to see who it was who had spoken with him. The would-be old man had completely disappeared, since he was an Angel sent by God to test the Saint's love.
Even a pious person is not immune to spiritual sickness if he does not have a wise guide -- either a living person or a spiritual writer. This sickness is called prelest, or spiritual delusion, imagining oneself to be near to God and to the realm of the divine and supernatural. Even zealous ascetics in monasteries are sometimes subject to this delusion, but of course, laymen who are zealous in external struggles (podvigi) undergo it much more frequently. Surpassing their acquaintances in struggles of prayer and fasting, they imagine that they are seers of divine visions, or at least of dreams inspired by grace. In every event of their lives, they see special intentional directions from God or their guardian angel. And then they start imagining that they are God's elect, and often try to foretell the future. The Holy Fathers armed themselves against nothing so fiercely as against this sickness -- prelest.
We must accomplish the course of our earthly pilgrimage with the greatest attention and watchfulness over ourselves, unceasingly calling upon God in prayer for help.
By holy baptism original sin is expunged, as also sins committed before baptism. It also eliminates the violent power sin has over us till rebirth; it gives us the grace of the Holy Spirit by which we are united with God in Christ, and we receive power to subdue and conquer sin. For the simple reason that we are not delivered from the struggle with sin, we cannot be entirely free from sin during the whole of our earthly life, and even the righteous man may fall seven times (i.e. often) and rise again by repentance, says Scripture (Prov. 24:16). He falls on account of his weakness and limitations, because he does not always notice sin which subtly and imperceptibly rears its head from his fallen nature, and which is artfully and imperceptibly offered and suggested by fallen spirits. Repentance becomes his secure possession, his constant weapon, his invaluable treasure. By repentance the righteous man maintains his fellowship with Christ. He is healed by repentance from the wounds caused by sin.
According to the teachings of the Holy Fathers, in order to destroy insensibility man needs a constant, patient, uninterrupted activity against insensibility; he needs a constant, pious, and attentive life.
An elder prescribes the following rule of conduct for the monastic table: 'When you sit to eat, brother, do not be overcome by the demon of gluttony, which compels you to eat in a disorderly way and in haste and to desire to taste many kinds of food together. Learn to eat modestly and in an orderly way and maintain a measure of restraint.'