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.
If you wish to be delivered from shameful passions, do not behave with anyone familiarly, especially with those toward whom your heart is inclined by a lustful passion; through this you will be delivered also from vainglory. For in vainglory is involved the pleasing of men, in the pleasing of men is involved familiarity of behavior, and familiarity of behavior is the mother of all passions.
The flow of history confirms the reality of the Gospel: the Church is filled to overflowing with sinners. Does their presence in the Church reduce, violate, or destroy her sanctity? Not in the least! For her Head—the Lord Christ, and her Soul—the Holy Spirit, and her divine teaching, her mysteries, and her virtues, are indissolubly and immutably holy. The Church tolerates sinners, shelters them, and instructs them, that they may be awakened and roused to repentance and spiritual recovery and transfiguration; but they do not hinder the Church from being holy. Only unrepentant sinners, persistent in evil and godless malice, are cut off from the Church either by the visible action of the theanthropic authority of the Church or by the invisible action of divine judgment, so that thus also the holiness of the Church may be preserved.
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.
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).
Do not neglect the practice of the virtues; if you do, your spiritual knowledge will decrease, and when famine occurs you will go down into Egypt (Genesis 41:57, 46:6).
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.
