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.
It took Noah a hundred years to build his ark; log upon log he dragged to the construction. Do as he did; drag log upon log to your construction, patiently, in silence, day after day, and do not inquire about your surroundings. Remember that Noah was the only on in the whole world who 'walked with God' (Gen. 6:9), that is, in prayer. Imagine the crowding, the darkness, the stench, that he had to live in until he could step out into the pure air and build an altar to the Lord. The air and the altar you will find within you, explains St. John Chrysostom, but only after you have willingly gone through the same narrow gate as Noah.
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.
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.
The weather shifts from cloudy to clear and then back to rain; thus it is with human nature. One must always expect clouds to hide the sun sometimes. Even the saints have had their dark hours, days and weeks. They say then that 'God has left them' in order that they may know truly how utterly wretched they are of themselves, without His support. These times of darkness, when all seems meaningless, ridiculous and vain, when one is beset by doubt and temptations, are inevitable. But even these times can be harvested for good. The dark days can best be conquered by following the example of St. Mary of Egypt. For forty-eight years she dwelt in the desert beyond Jordan, and when temptations befell her and memories of her former sinful life in Alexandria beckoned her to leave her voluntary sojourn in the desert, she lay on the ground, cried to God for help and did not get up until her heart was humbled. The first years were hard; she sometimes had to lie this way for many days; but after seventeen years came the time of rest. On such days stay quiet. Do not be persuaded to go out into social life or entertainment. Do not pity yourself, seek comfort in nothing but your cry to the Lord: 'Haste thee, O God, to deliver me! Makes haste to help me, O Lord (Psalm 70:1)! I am so fast in prison that I cannot get forth (Psalm 88:8),' and other such appeals. You cannot expect real help from any other source. For the sake of chance relief do not throw away all your winnings. Pull the covers over your head; now your patience and steadfastness are being tried. If you endure the trial, thank God who gave you the strength. If you do not, rise up promptly, pray for mercy and think: I got what I deserved! For the fall itself was your punishment. You had relied too much on yourself, and now you see what it led to. You have had an experience; do not forget to give thanks.
The soul of all practices in the Lord is vigilance. Without vigilance, all these practices are fruitless. He who is desirous of saving himself must so establish himself that he might remain continuously vigilant toward himself, not only in solitude, but also under conditions of distraction, into which he is sometimes unwillingly drawn by circumstances.
But if you are fearful of becoming self-righteous from working for your own salvation, or afraid of being overcome by spiritual pride, examine yourself and observe that the person who is afraid of becoming self-righteous suffers from blindness. For he does not see how self-righteous he is.
My child, do you want to crush the head of the serpent? Openly reveal your thoughts in confession. The strength of the devil lies in cunning thoughts. Do you hold on to them? He remains hidden. Do you bring them to the light? He disappears. And then Christ rejoices, the prayer progresses, and the light of grace heals and brings peace to your nous and heart.
You must set about rooting out the very desire to have things pleasant, to get on well, to be contented. You must learn to like sadness, poverty, pain, hardship. You must learn to follow privately the Lord's bidding: not to speak empty words, not to adorn yourself, always to obey authority, not to look at a woman with desire, not to be angry and much else. For all these biddings are given us not in order for us to act as if they did not exist, but for us to follow: otherwise the Lord of mercy would not have burdened us with them. If any man will come after me, let him deny himself, He said (Matthew 16:24), thereby leaving it to each person's own will-if any man will-and to each person's endeavor: let him deny himself.
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…
The power given by the Lord to His seventy disciples is given to all Christians (Mk. 16:17). Use it, Christian! With the name of Jesus cut off their heads, that is the first appearances of sin in our thoughts, fancies and feelings. Destroy within you the devil's rule over you; destroy all his influence over you; acquire spiritual freedom. The foundation for your struggle is the grace of holy baptism; your weapon is prayer in the name of Jesus.