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.
When the flesh flourishes, the soul fades; when the flesh has full liberty, the soul is straitened; when the flesh is satiated, the soul hungers; when the flesh is adorned, the soul is deformed; when the flesh overflows with laughter, the soul is surrounded by misfortune; when the flesh is in the light, the soul is in darkness...
The body can neither love nor hate. Neither can a body fall in love with a body. The capability for love belongs to the soul. When the soul is in love with the body, that is not love but desire, lust. When the soul is in love with the soul, but not through God, that is either admiration, or pity. However, when the soul, through God loves the soul, without consideration for the appearance of the body - beauty or ugliness - that is love. That is true love. For in love is life.
When the flesh flourishes, the soul fades; when the flesh has full liberty, the soul is straitened; when the flesh is satiated, the soul hungers; when the flesh is adorned, the soul is deformed; when the flesh overflows with laughter, the soul is surrounded by misfortune; when the flesh is in the light, the soul is in darkness...
Our soul is simple as thought, and rapid as thought or lightning. In an instant it can be wounded by sin and become attached to corruptible things; in an instant it can fall away from the love of God and its neighbor through a single unrighteous thought, through a single passionate desire, through a single malevolent thought, and, therefore, we must constantly watch our heart, lest it should incline to words or thoughts of evil, and must ever strive to preserve it in God's simplicity and purity, and in the love of God and its neighbor.
Charity, temperance, contemplation, and prayer please God; gluttony, licentiousness, and what multiplies them, please the flesh. Therefore they who are in the flesh cannot please God. And they that are Christ’s have crucified their flesh with the passions and concupiscences.
Use your body, I beseech you, with moderation. Remember, with this body you will be raised from death when you come to be judged. Perhaps you have some doubt whether this could happen. If so, reflect in detail on what has already happened with your own self. Tell me, where were you a hundred years ago? Cannot the Creator who gave existence to a person that did not exist bring to life again to a person that did exist but is now dead? Every year He makes the corn spring to life that had withered and dies after it was sown. Do you suppose that He who raised Himself from the dead for our sake will have difficulty in raising us to new life? Or look at the trees. For a number of months they remain without fruit, even without leaves. But once the winter is past, they become green all over, new, as if risen from the dead. With better reason, and with greater ease shall we be called to new life. Do not listen to those who deny the resurrection of the body. Isaiah testifies: ‘The dead shall live again: the bodies of those who have died shall live.’ (Isa. 26:19) And according to the word of Daniel, ‘Many of those who sleep beneath the earth shall awaken, some to life eternal, the rest to eternal ruin.’ (Dan. 12:2)
Every day you provide your bodies with good to keep them from failing. In the same way your good works should be the daily nourishment of your hearts. Your bodies are fed with food and your spirits with good works. You aren't to deny your soul, which is going to live forever, what you grant to your body, which is going to die.