The man who does not humble himself and does not cleanse his heart from evil desires fasts in vain. He may eat nothing at all, but it will be to no avail if there is evil inside him. He must first cleanse himself from the evil within in order to receive the Lord.
What is self-justification? - Self-justification is when a man denies his sin, as we see in the case of Adam, Eve, Cain and others who have sinned but, wishing to justify themselves, denied their sin.
One should nourish the soul with the word of God: for the word of God, as St. Gregory the Theologian says, is angelic bread, by which are nourished souls who hunger for God. Most of all, one should occupy oneself with reading the New Testament and the Psalter, which one should do standing up. From this there occurs an enlightenment in the mind, which is in the mind, which is changed by a Divine change.
Remember, O my soul, the terrible and frightful wonder: that your Creator for your sake became Man, and deigned to suffer for the sake of your salvation. His angels tremble, the Cherubim are terrified, the Seraphim are in fear, and all the heavenly powers ceaselessly give praise; and you, unfortunate soul, remain in laziness. At least from this time forth arise and do not put off, my beloved soul, holy repentence, contrition of heart and penance for your sins.
When we return to prayer after a period of reading we find a rejuvenated and invigorated soul, stirred by the desire for God. The best form of prayer is one that implants the clearest idea of God in the soul and thus makes space for the presence of God within us. We become a temple of God when our continuous meditation on Him is not constantly interrupted by ordinary worries, and the spirit is not disturbed by unexpected emotions. Thus, in flight from all things, the spirit who loves God can approach God who drives out everything that leads us to evil, and holds steadfastly to everything that leads to virtue.
Trials are of two kinds. Either affliction will test our souls as gold is tried in a furnace, and make trial of us through patience, or the very prosperity of our lives will oftentimes, for many, be itself an occasion of trial and temptation. For it is equally difficult to keep the soul upright and undefeated in the midst of afflictions, as to keep oneself from insolence and pride in prosperity.
What should one do so that the mind might be constantly occupied with God? If we do not acquire the three following virtues: love for God and men, continence, and the Prayer of Jesus, then our mind cannot be completely occupied with God. For love makes anger meek, continence weakens fleshly desire, and prayer draws the mind away from thoughts and banishes every hatred and high-mindedness.
One cannot approach the knowledge of the truth with a disturbed heart. Therefore we must try to avoid everything that disturbs our heart, that causes forgetfulness, excitement or passion, or that awakens unrest. We must free ourselves as much as possible from all fuss and flutter and ado over vain things. Yes, when we serve the Lord we shall not be troubled about many things, but always keep in mind that one thing is needful (Luke 10:41).
Therefore, if you wish to conquer the passions, cut off the love of pleasure; but if you are pursuing food, you will spend a life in passions; the soul will not be humbled if the flesh is not deprived of bread. It is not possible to deliver the soul from perdition while protecting the body from unpleasantness.
To act 'according to one’s strength' means to use a little less than necessary both of food, and drink, and sleep... As for food, restrain yourself when you wish to eat a little more, and in this way you will always make use of it moderately.
Peace is the beginning of the purification of the soul, the tongue freed from speaking of the things of men, the eyes no longer dwelling on the beauty of bodies and elegance of our surroundings, the hearing not undoing the strength of the soul through listening to melodies that were composed for pleasure, nor through the talk of clever and frivolous men, which more than anything else has power to undo the purpose of the soul. For the mind, when not wasted on outward things, or led astray by the world of the senses, turns itself on itself, and through this ascends to the thought of God, and lit by that inward beauty becomes unmindful even of nature, and no more troubled by anxiety for its food, or with concern for clothing; at rest from earth’s cares, all its zeal is given to gaining the things that are good forever.
Watch constantly, learning to understand God's law, for this warms the heart with heavenly fire. Guard your lips from the idle word, or empty talk, lest the heart gets used to evil words.
Concerning fasting, do not grieve, as I have said to you before: God does not demand of anyone labors beyond his strength. And indeed, what is fasting if not a punishment of the body in order to humble a healthy body and make it infirm for passions, according to the word of the Apostle: 'When I am weak, then am I strong' (II Corinthians 12:10).
One must clean the royal house from every impurity and adorn it with every beauty, then the king may enter into it. In a similar way one must cleanse the earth of the heart and uproot the weeds of sin and the passionate deeds and soften it with sorrows and the narrow way of life, sow in it the seed of virtue, water it with lamentation and tears, and only then does the fruit of dispassion and eternal life grow. For the Holy Spirit does not dwell in a man until he has been cleansed from passions of the soul and body. Only one thing may remain within a man, either the Holy Spirit or the passions. Where the Holy Spirit is, there the passions do not come near, and where the passions are, there the Holy Spirit does not dwell, but rather the evil one.