Saint Nicodemos The Hagiorite
Just as it is necessary to guard the mind from ignorance, so is it equally necessary to protect it from the opposite, namely from too much knowledge and curiosity. For if we fill it with a quantity of information, ideas and thoughts, not excluding such as are vain, unsuitable and harmful, we deprive it of force, so that it is no longer able to understand clearly what is useful for our true self-correction and perfection. Therefore, in relation to the knowledge of earthly things, which is not indispensable, even if it is permissible, your attitude should be as of one already dead. Always collect your mind within yourself, with all the concentration you can, and keep it free of thoughts about all worldly things.
Let tales of the past and news of the present pass you by, and let all the changes in the world and its kingdoms, be for you as though they did not exist at all. If anyone brings you such news, disregard it and turn it away from your heart and imagination. Listen to what St. Basil says: "Let listening to worldly news be bitter food for you, and let the words of saintly men be as combs filled with honey.” Listen also to the words of David: "The proud have digged pits for me, which are not after thy law" (Psalm 109:85). Love to hear only of spiritual and heavenly things and to study them, and wish to know nothing in the world except our Lord "Jesus Christ, and Him crucified" (I Corinthians 2:2), save His life and death and what He demands of you. Acting thus, you will act in a way pleasing to God, Who has for His chosen and beloved those who love Him and try to do His will.
All other inquiry and investigation is the offspring and food of self-love and pride. They are the nets and shackles of the devil; he sees the strength and firmness of will of those who pay attention to spiritual life, and strives to conquer their minds by means of such curiosity, in order to gain possession of their mind and will. For this purpose, he suggests to them thoughts that are lofty, subtle and wondrous, especially to those who are sharp-witted and quick to make lofty speculations. Attracted by the pleasure of possessing and examining such lofty thoughts, they forget to watch over their purity of heart and to pay attention to a humble opinion of themselves and to true self-mortification; and so they are enmeshed in the bonds of pride and conceit; they make an idol of their own mind and thus, little by little, without realizing it, they fall into the thought that they no longer need any advice or admonition from others, since they are accustomed in all cases to hasten to the idol of their own understanding and judgment.
This is a very dangerous thing and not easily cured; pride of mind is much worse than pride of will. For pride of will, being visible to the mind, can sometimes be easily cured by forcing it to submit to the yoke of what is good. But when the mind is firmly grounded in the self-relying thought that its own judgments are better than all others, who can cure it in the end? Can it ever obey anyone, if it feels certain that the judgments of others are not as good as its own? When this eye of the soul -- mind -- with whose help man could see and correct pride of will, is itself blinded by pride and remains uncured, who will cure the will? Then every thing within is so disorganized that there is neither place nor person for applying a healing poultice. This is why you must hasten to oppose this pernicious pride of mind, before it penetrates into the marrow of your bones. Resist it, curb the quickness of your mind and humbly subject your opinion to the opinions of others. Be a fool for the love of God, if you wish to be wiser than Solomon. "If any man among you seems to be wise in this world, let him become a fool, that he may be wise." (I Corinthians 3:18)
"Unseen Warfare," by St. Nicodemos of the Holy Mountain, revised by St. Theophan the Recluse