No man, wise in his own opinion, because he has studied all the sciences and is learned in external wisdom, will ever penetrate God's mysteries or see them unless he first humbles himself and becomes foolish in his heart, repudiating his self-opinion together with his acquirements of learning. For a man who acts thus and follows with undaunted faith those who are wise in things Divine, is guided by them and with them enters into the city of the living God, and, taught and enlightened by the Holy Spirit, sees and knows things which no one else can see or know. Thus he becomes taught of God.
ST. SIMEON THE NEW THEOLOGIAN Philokalia, Practical and Theological Precepts