Observe your thoughts, and beware of what you have in your heart and your spirit, knowing that the demons put ideas into you so as to corrupt your soul by making it think of that which is not right, in order to turn your spirit from the consideration of your sins and of God.
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.
When you intend to do something and see that your thought is perturbed, and if after invoking God's Name it remains perturbed even by a hair's breadth, know from this that the action you mean to commit is from the evil one and refrain from commiting it. For nothing done with perturbation is pleasing to God.
When tested by some trial you should try to find out not why or through whom it came, but only how to endure it gratefully, without distress or rancor.
When an archer desires to shoot his arrows successfully, he first takes great pains over his posture and aligns himself accurately with his mark. It should be the same for you who are about to shoot the head of the wicked devil. Let us be concerned first for the good order of sensations and then for the good posture of inner thoughts.
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.
Let us avail ourselves of the example of that holy staretz who used to say: 'Depart, evil one; come, beloved!' Once a brother who overheard his words and supposed that the staretz was speaking to another man asked him 'With whom are you conversing, father?' And the staretz answered: 'I am driving away evil thoughts and calling the good ones to my side.' And so, if we are tempted, let us use the words of that staretz, or others like them.
Knowing the exact nature of everything, God permits each person to be tested according to his strength. As St. Paul puts it: 'God is to be trusted not to let you be tried beyond your strength, but with the trial He will provide a way out, so that you are able to bear it' (1 Cor. 10:13).
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.