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.
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.
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.
Just as the arena and the field of action tests the athlete, so also the Christian is checked in the arena of struggle as to whether he truly loves God. Patience in the struggle against various sins and courage in rushing out to apply the divine commandments characterize the fervent worshipper of Jesus.
Continually say the Prayer [of Jesus] intensely, with zeal, with longing; only thus does one become strong in soul. Avoid idle words by means of all sacrifice, for they weaken the soul and it does not have the strength to struggle.
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 ... and to each person's endeavor: let him deny himself.
The way to attain compunction is an attentive life. ‘The beginning of repentance comes from the fear of God and attention,’ as the holy martyr Boniface says.
Those who have acquired genuine prayer experience an ineffable poverty of the spirit when they stand before the Lord, glorify and praise Him, confess to Him, or present to Him their entreaties. They feel as if they had turned to nothing, as if they did not exist. That is natural. For when he who is in prayer experiences the fullness of the divine presence, of Life Itself, of Life abundant and unfathomable, then his own life strikes him as a tiny drop in comparison to the boundless ocean. That is what the righteous and long-suffering Job felt as he attained the height of spiritual perfection. He felt himself to be dust and ashes; he felt that he was melting and vanishing as does snow when struck by the sun's burning rays (Job 42:6).
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…
He stands, then - but not alone, for before Him go angels, saying: 'Lift up the gates, O ye the princes.' What gates? Even those of which the Psalmist sings in another place also: 'Open to me the gates of righteousness.' Open, then, thy gates to Christ, that He may come into thee - open the gates of righteousness, the gates of chastity, the gates of courage and wisdom. Believe the message of the angels: 'Be ye lifted up, ye everlasting doors, and the King of Glory shall come in, the Lord of Sabaoth.'
The Holy Fathers teach us how to become familiar with the Gospel, how to read it and how to understand it, what helps and what opposes its understanding. Therefore, at first you must devote more time to reading the Holy Fathers...
To the world belong our desires and impulses. enumerates them: Weakness for wealth and for collecting and owning things of different kinds; the urge for physical (sensuous) enjoyment; the longing for honor, which is the root of envy; the desire to conquer and be the deciding factor; pride in the glory of power; the urge to adorn oneself and to be liked; the craving for praise; concern and anxiety for physical well-being. All these are of the world; they combine deceitfully to hold us in heavy bonds. If you wish to free yourself, scrutinize yourself with the help of that list and see clearly what you have to struggle against in order to approach God. For friendship with the world is enmity with God, and whosoever therefore will be a friend of the world is the enemy of God (James 4:4).