I have just finished reading The Ladder of Divine Ascent written by Saint John Climacus. I would recommend the book to study early church monasticism, disciplines, discernment, virtue and vices. In addition I have just finished reading God's revelation to the human heart written by now Saint Seraphim Rose which I would recommend, he is a great newly canonized contemporary Saint by ROCOR and his writings have pricked me to the heart. This one asks the question of why one studies religion? How does God reveal himself to different people, the nature of suffering, and the spiritual rebirth. I'm about to start on Nihilism the revolution of the modern age written by Saint Seraphim Rose. Stay in the scriptures, constantly study the fathers, stay in prayer, fasting, and stay in the life of the church.