On how we should exercise our mind, lest it be sick with the disease of ignorance
If disbelief in oneself and trust in God, so indispensable in our spiritual warfare, remain alone in us, not only shall we never gain victory, but we shall fall into still greater evil. For in addition and accompanying them we must practise works of a special kind and perform exercises in spiritual instruction. First among these must be exercises of mind and will. The mind should be freed and guarded from ignorance, which is most harmful, for it darkens the mind and prevents it from knowing the truth, which is its proper object and the aim of its aspirations. For this reason it should be exercised, to make it clear and lucid, able to discern correctly what we need to purify our soul from passions and to adorn it with virtues.
There are two means by which we can acquire such clarity of mind: the first and most necessary is prayer, by which we must implore the Holy Spirit to pour His divine light into our hearts. This He will surely do, if we truly seek God alone and sincerely strive to obey His will in everything, willingly submitting in all affairs to the advice of our experienced spiritual fathers and doing nothing without asking them.
The second method of exercising the mind is always to examine things and probe deep for knowledge of them, in order to see clearly which of them are good and which bad.. We should judge them not as the world and the senses do, but as they are judged by right season and the Holy Spirit, or by the word of the divinely-inspired Scriptures, or that of the holy fathers and teachers of the Church. For if this examination and deepening of knowledge is right and proper, it will quite certainly enable us to understand clearly that we must with all our heart regard as valueless, vain and false, all that the blind and depraved world loves and seeks. In particular, we shall then see that the honours, pleasures and riches of this world are nothing but vanity and death to the soul; that the slander and abuse, with which the world persecutes us, bring us true glory, and its afflictions—joy; that to forgive our enemies and to do good to them is true magnanimity—one of the greatest traits of likeness to God; that a man who scorns the world shows greater strength and power than a man who rules over the whole world; that willing obedience is an action, which shows more courage and strength of spirit than subjugating great kings and ruling over them; that humble self-knowledge should be preferred to all other kinds of knowledge, however high; that to overcome and kill one’s own evil tendencies and lusts, however insignificant, is more worthy of praise than the capture of many fortresses, or the defeat of powerful and well-equipped armies; more even than the power to perform miracles and to raise the dead.