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.
Fasting, while of value in itself, is not something to boast of in front of God, for it is simply a tool for training those who desire self-restraint. The ascetic should not feel proud because he fasts; no artist ever boasts that his accomplishment is simply due to his tools; but he waits for the work itself to give proof of his skill.
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).
To those who are just beginning to long for holiness, the path of virtue seems very rough and forbidding. It appears like this, not because it really is difficult, but because our human nature from the womb is accustomed to the wide roads of sensual pleasure. But those who have traveled more than half its length find the path of virtue smooth and easy. For when a bad habit has been subjected to a good one through the energy of grace it is destroyed along with the remembrance of mindless pleasures; and thereafter the soul gladly journeys on all the ways of virtue. At the beginning of the struggle, therefore, the holy commandments of God must be fulfilled with a certain forcefulness of will (cf. Matt. 11:12); then the Lord, seeing our intention and labor, will grant us readiness of will and gladness in obeying His purpose. For 'it is the Lord who makes ready the will' (Prov. 8:35, LXX), so that we always do what is right joyfully. Then shall we truly feel that 'it is God who energizes in you both the willing and the doing of His purpose' (Phil. 2:13).
If anyone thinks that he has love but does not have the same love for all, but distinguishes between persons, separating the lowly from the rich, the infirm from the healthy, a sinner from a righteous man, one far off from one near, one who is an enemy from one who loves you, such love is not perfect, but partial. Actual and perfect love consists in considering everyone and loving them equally, both those who love you and those who hate you. Such love, with which mercy is inseparable, is, in brief, a net for all virtues. It embraces and contains all the commandments of God within itself.
Let us have recourse to humility on all occasions; for the humble lie prone on the ground, and how can a man fall if he lies on the ground? But a man who stands on a height can easily fall.
If we fervently desire holiness, the Holy Spirit at the outset gives the soul a full and conscious taste of God’s sweetness, so that the intellect will know exactly of what the final reward of the spiritual life consists.
Silence of lips is better and more wonderful than any edifying conversation. Strive to acquire humility and submissiveness. Never insist that anything should be according to your will, for this gives birth to anger. Do not judge or humiliate anyone, for this gives birth to anger. Do not judge or humiliate anyone, for this exhausts the heart and blinds the mind, and thereon leads to negligence and makes the heart unfeeling.
For the complete fulfillment of its [the intellect's] purpose we should give it nothing but the prayer 'Lord Jesus'...Those who meditate unceasingly upon this glorious and holy name in the depths of their heart can sometimes see the light of their own intellect. For when the mind is closely concentrated upon this name, then we grow fully conscious that the name is burning up all filth which covers the surface of the soul; for it is written: 'our God is a consuming fire' (Deut. 4:24). Then the Lord awakens in the soul a great love for His glory...This is the pearl of great price which a man can acquire by selling all that he has, and so experience the inexpressible joy of making it his own.
If thou, being offended by anything, dost sense that grief and wrath have seized thee, preserve silence, and say naught until unceasing prayer pacifies thine heart.
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.
My brother, the passions are afflictions; and so the Lord does not excommunicate us because of them, but He says: 'Call upon me in the time of affliction; and I will deliver thee, and thou shalt glorify me'. Therefore, when beset by any kind of passion, there is nothing more useful than to call upon the Name of God. All we can do, weak as we are, is to flee for refuge to the Name of Jesus. For the passions, being demons, retreat if this Name is invoked.
Acquire humility, which scorches the demons, obedience, which opens the door for the Son of God to enter a man, faith which saves a man, hope which makes him unashamed; and love which lets not a man fall away from God.
It is well known that obedience is the chief among the initiatory virtues, for first it displaces presumption and then it engenders humility within us. Thus it becomes, for those who willingly embrace it, a door leading to the love of God. It was because he rejected humility that Adam fell into the lowest depths of Hades. It was because He loved humility that the Lord, in accordance with the divine purpose, was obedient to his His Father even to the cross and death, although He was in no way inferior to the Father; and so through His obedience He has freed mankind from the crime of disobedience and leads back to the blessedness of eternal life all who live in obedience. Thus humility should be the first concern of those who are fighting the presumption of the devil, for as we advance it will be a sure guide to all the paths of virtue.
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.