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.
Unless humility and love, simplicity and goodness regulate our prayer, this prayer - or, rather, this pretence of prayer - cannot profit us at all. And this applies not only to prayer, but to every labor and hardship undertaken for the sake of virtue.
The good man thinks to himself in this wise: Every one who has strayed from the truth brings destruction on himself and is therefore to be pitied. But of course the man who has not learned the love of the Holy Spirit will not pray for his enemies. The man who has learned love from the Holy Spirit sorrows all his life over those who are not saved, and sheds abundant tears for the people, and the grace of God gives him strength to love his enemies.
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.
My son, says Scripture, if you come to serve the Lord, prepare your soul for trial, set you heart straight, and patiently endure (Eccles. 2:1-2). And elsewhere it is said: Accept everything that comes as good, knowing that nothing occurs without God willing it. Thus the soul that wishes to do God's will must strive above all to acquire patient endurance and hope. For one of the tricks of the devil is to make us listless at times of affliction, so that we give up our hope in the Lord. God never allows a soul that hopes in Him to be so oppressed by trials that it is put to utter confusion. As St. Paul writes: God is to be trusted not to let us be tried beyond our strength, but with the trial He will provide a way out, so that we are able to bear it (I Cor. 10:13). The devil harasses the soul not as much as he wants but as much as God allows him to. Men know what burden may be placed on a mule, what on a donkey, and what on a camel, and load each beast accordingly; and the potter knows how long he must leave the pots in the fire, so that they are not cracked by staying in it too long or rendered useless by being taken out of it before they are properly fired. If human understanding extends this far, must not God be much more aware, infinitely more aware, of the degree of trial it is right to impose on each soul, so that it become tried and true, fit for the kingdom of heaven?
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.
The soul that really loves God and Christ, though it may do ten thousand righteousnesses, esteems itself as having wrought nothing, by reason of its insatiable aspiration after God. Though it should exhaust the body with fastings, with watchings, its attitude towards the virtues is as if it had not even begun to labor for them.
When you receive from Heaven the gift of patience, be attentive and vigilant over yourself, so as to hold and keep within yourself the grace of God, lest sin should creep unnoticed into your soul or body and drive away this grace.
This is the mark of Christianity--however much a man toils, and however many righteousnesses he performs, to feel that he has done nothing, and in fasting to say, 'This is not fasting,' and in praying, 'This is not prayer,' and in perseverance at prayer, 'I have shown no perseverance; I am only just beginning to practice and to take pains;' and even if he is righteous before God, he should say, 'I am not righteous, not I; I do not take pains, but only make a beginning every day.'
Many are the obstacles that stand in the way of pleasing God; for not merely poverty and obscurity but also riches and honor are trials for the soul. Indeed, to some extent even the solace and ease which grace bestows on the soul can easily become a temptation and a hindrance if the soul is not properly conscious of these effects of grace and does not enjoy them with great circumspection and understanding: for the spirit of evil tries to persuade the soul to relax now it possesses grace, and so contrives to implant in it sluggishness and apathy.
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.
Inside us evil is at work suggesting unworthy inclinations. However, it is not in us in the same way as, to take as an example, water mixes with wine. Evil is in us without being mixed with good. We are a field in which wheat and weeds are growing separately. We are a house in which there is a thief, but also the owner. We are a spring which rises from the middle of the mud, but pours out pure water. All the same, it is enough to stir up the mud and the spring is fouled. It is the same with the soul. If the evil is spread, it forms a unity with the soul and makes it dirty. With our consent, evil is united with the soul; they become accomplices. Yet there comes a moment when the soul can free itself and remain separate again: in repentance, contrition, prayer, recourse to God. The soul could not benefit from these habits if it were always sunk in evil. It is like a marriage. A woman is united with a man and they become one flesh. But when one of them dies, the other is left alone. But union with the Holy Spirit is complete. So, let us become a single spirit with Him. Let us be wholly absorbed by grace.
She dwells in heaven and continually beholds the glory of God, yet she does not forget us, poor wretches that we are, and spreads her compassion over the whole earth and all peoples. And this most pure Mother of His the Lord has bestowed on us. She is our joy and our expectation. She is our mother in the spirit, and kin to us by nature as a human being, and every Christian soul leaps to her in love.
If you are enclosed within yourself through prayer, humility, and mourning, you will find a spiritual treasure -- only let pride and criticism be far from you.