As a man cannot remain unscathed who spares his enemy on the field of battle, so a man engaged in spiritual warfare cannot save his soul if he spares his body.
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…
Just as we must beware of overeating, so too we must beware of excessive temperance or abstinence. Excessive temperance weakens the body, destroys wakefulness, coolness and freshness which are indispensable for vigilance, and which fade and weaken when the physical powers succumb and fail. If you force a weak body to labor beyond its powers, you subject your soul to double darkness, and lead it into confusion (and not relief)...
One must train oneself in self-reproach, that is, always accuse oneself & not others in one’s mind, reproach oneself and not others, and with a severe distrust of oneself accuse oneself of the failings which are covered up by our self-love, accuse ourself of our inclinations to sin. He who has self-reproach has peace, writes Abba Dorotheos, & will never be disturbed. If to such a one there should occur an illness, a wrong, a vexation, or some similar misfortune, he ascribes everything to his own sins & thanks God. If such a one is punished or reprimanded by the superior, he accepts all this as good & accepts every severe word against himself without murmuring or talking back, as the judgment of God.
Do not regard the feelings of a person who speaks to you about his neighbor disparagingly, but rather say to him: 'Stop, brother! I fall into graver sins every day, so how can I criticize him?' In this way you will achieve two things: you will heal yourself and your neighbor with one plaster. This is one of the shortest ways to the forgiveness of sins; I mean, not to judge. 'Judge not, and ye shall not be judged,' (Luke 6:37).
A prayer offered while one has any cause to reproach a fellow man is an impure prayer. There is only one whom the praying person may and must reproach, and that is himself. Without self-reproach, your prayer is as worthless as it is while you are reproaching someone else in your heart. Perhaps you ask: How can one learn this? The answer is: One learns it through prayer.
The first duty of a Christian, of a disciple and follower of Jesus Christ, is to deny oneself. To deny oneself means to give up one's bad habits, to root out of the heart all that ties us to the world; not to cherish bad desires and thoughts; to quench and suppress bad thoughts; to avoid occasions of sin; not to do or desire anything from self-love but to do everything out of love for God. To deny oneself means, according to the Apostle Paul, to be dead to sin and the world, but alive to God.