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.
So long as the soul is sick with passions, its senses have no perception of the spiritual; and the soul does not even know how to desire it, but desires it only from hearsay and writings. The power of the soul is cured of these diseases by the hidden practice of commandments, with sharing in Christ's passion.
If the main goal of the repentant sinner should be total, light-bearing and blessed communion with God, then the main hindrance to this is the existence of the passions still active and working in him - the virtues being as yet unsealed in him - and the unrighteousness of his powers. Therefore his main work upon conversion and repentance should be the uprooting of the passions and sealing the virtues - in a word, correcting himself.
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.
If we cut off the causes of the passions for only a short while, and occupy ourselves with spiritual contemplation without making it our sole and constant concern, we easily revert to the passions of the flesh, gaining nothing from our labor but theoretical knowledge coupled with conceit. The result is a gradual darkening of this knowledge itself and a complete turning of the intellect towards material things.
When a passion arises, when it is young and feeble, cut it off, lest it stiffen and cause you a great deal of trouble. It is one thing to pluck out a small weed and quite another thing to uproot a great tree.
Therefore, if you wish to conquer the passions, cut off the love of pleasure; but if you are pursuing food, you will spend a life in passions; the soul will not be humbled if the flesh is not deprived of bread. It is not possible to deliver the soul from perdition while protecting the body from unpleasantness.
If Nabuzardan, the court cook of the King of the Babylonians, had not gone to Jerusalem, then the Temple would not have burned (cf. 2 Kings 24), That is to say, a person’s mind is not attacked by the flames of carnal pleasures, if a person is not conquered by gluttony.
Unless the inner man meditates upon the law of God and is nourished thereby, unless he is strengthened by reading and by prayer, he is conquered by the outer man, and he serves his master.
How can one say that a man has attained purity? - When he sees all men as being good, and when none appears to him to be unclean and defiled - then he is indeed pure in heart.