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.
Blessed are the pure in heart, for they shall see God. Everything we do, our every objective, must be undertaken for the sake of this purity of heart. This is why we take on loneliness, fasting, vigils, work, nakedness. For this we must practice the reading of the Scripture, together with all the other virtuous activities, and we do so to trap and to hold our hearts free of the harm of every dangerous passion and in order to rise step by step to the high point of love.
God seeks nothing else from us men except that we do not sin; this alone. But this is not a work of law; it is rather a careful guarding of the image and dignity from above. In these things, affirmed in our nature and bearing the radiant garment of the Spirit, we shall abide in God and He in us. We shall be called good, and sons of God by adoption, marked in the light of our knowledge of God.
There is a sin which is always 'unto death' [1 Jn 5:16]; the sin which we have not repented. Even a saint's prayers will not be heard for the unrepented sin. The person who repents correctly does not imagine that his sins are cancelled through his own effort; but knows that through this effort he makes peace with God.
If however any one thinks that he is not being burned when sinning, to him the Scripture saith, Shall a man wrap up fire in his bosom, and not burn his clothes? For sin burns the sinews of the soul, and breaks the spiritual bones of the mind, and darkens the light of the heart.
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...
Greater therefore is the rejoicing of heaven over the sinner converted than upon the soul that remained just. A captain in battle will feel a warmer regard for the soldier who at first faltered and ran, and then had bravely fought back, than over the one who had never yielded yet had never thrust bravely forward. So will the farmer love more the fields that cleaned of their weeds now bear a fruitful yield, than the land which had never known thorns, yet had never yielded a bountiful crop.
Those who have sinned must not despair. Let that never be. For we are condemned not for the multitude of evils, but because we do not want to repent...
Unless curbed by the fear of God that accompanies the practice of the virtues, spiritual knowledge leads to vanity; for it encourages the person puffed up by it to regard as his own what has merely been lent to him, and to use his borrowed intelligence to win praise for himself. But when his practice of the virtues increases concomitantly with his longing for God, and he does not arrogate to himself more spiritual knowledge than is needed for the task in hand, then he is made humble, reduced to himself by principles which are beyond his capacity.