Fear God and keep His commandments both in your feelings and in your intellect. If you force yourself to keep them in your intellect, bit by bit you will attain to fulfilling them in your feelings.
To wage war only with the sins that make their appearance as actual deeds would be just as unsuccessful as cutting down weeds in a garden instead of digging them up at the root and throwing them out. Sins appear as inevitable outgrowths from their roots, the passions of the soul.
The heart which is constantly guarded, and is not allowed to receive the forms, images and fantasies of the dark and evil spirits, is conditioned by nature to give birth from within itself to thoughts filled with light. For just as coal engenders a flame, or a flame lights a candle, so will God, who from our baptism dwells in our heart, kindle our mind to contemplation when He finds it free from the winds of evil and protected by the guarding of the intellect.
The Lord said, 'When you have done all that is commanded you, say: We are useless servants: we have only done what was our duty' (Luke 17:10). Thus the kingdom of heaven is not a reward for works, but a gift of grace prepared by the Master for His faithful servants.
It is impossible for the soul to attain anything spiritual and pleasing to God, or to be free of inner sin, without guarding of the mind and purity of heart, in other words, without sobriety... If with God's help we gain something daily through our sobriety, we should take care not to enter into communication with other people without discrimination, lest we suffer loss through our converse with them and are led into temptation.
Prayer... by its action it is the reconciliation of man with God, the mother and daughter of tears, a bridge for crossing temptations, a wall of protection from afflictions, a crushing of conflicts, boundless activity, the spring of virtues, the source of spiritual gifts, invisible progress, food of the soul, the enlightening of the mind, an axe for despair, a demonstration of hope, the release from sorrow.
Even a pious person is not immune to spiritual sickness if he does not have a wise guide -- either a living person or a spiritual writer. This sickness is called prelest, or spiritual delusion, imagining oneself to be near to God and to the realm of the divine and supernatural. Even zealous ascetics in monasteries are sometimes subject to this delusion, but of course, laymen who are zealous in external struggles (podvigi) undergo it much more frequently. Surpassing their acquaintances in struggles of prayer and fasting, they imagine that they are seers of divine visions, or at least of dreams inspired by grace. In every event of their lives, they see special intentional directions from God or their guardian angel. And then they start imagining that they are God's elect, and often try to foretell the future. The Holy Fathers armed themselves against nothing so fiercely as against this sickness -- prelest.
Therefore with your whole soul you should acknowledge yourself as worthy of enduring more than you already endure; remember the words which Christ the Savior spoke concerning a good deed done to one's neighbor, words which should apply equally to every offensive word or deed against one's neighbor. Whatever you have done to your neighbor, He says, you have done to Me.
St. John Climacus was asked if there are reliable signs by which it's possible to know whether a soul is drawing near to God or moving away from Him. After all, regarding ordinary things there are clear signs as to whether they're good or not. When, for instance, cabbage, meat or fish begins to rot, it's easy to notice it, since the rotting object begins to give off a foul odor, the color and taste change, and its external appearance witnesses to its deterioration. Well, and what about the soul? After all, it's bodiless and can't give off a bad smell or change its appearance. To this question the Holy Father replies, 'A sure sign of the deadening of the soul is the avoidance of church services.'
We should zealously cultivate watchfulness, my brethren; and when, our mind purified in Christ Jesus, we are exalted by the vision it confers, we should review our sins and our former life, so that shattered and humbled at the thought of them we may never lose the help of Jesus Christ our God in the invisible battle.
Whenever we are filled with evil thoughts, we should throw the invocation of our Lord Jesus Christ in their midst. Then, as experience has taught us, we shall see them instantly dispersed like smoke in air. Once the intellect is left to itself again, we can renew our constant attentiveness and our invocation. Whenever we are distracted, we should act in this way.
When the enemy tempts you with thoughts of faithlessness, with all your heart say, I believe completely whatever the Church believes, whatever Christ says in the Holy Gospels, whatever the Holy Apostles and the Holy Fathers said. 'I don't, however, believe you, devil, for you are a liar and a thief.'