His theological works emphasize the empirical basis of theology called theoria or vision of God, (as opposed to intellectual-contemplative) as the essence of Orthodox Theology. He identified Hesychasm as the core of Christian practice and studied extensively the works of 14th century hesychast and theologian St. Gregory Palamas.

His research on Dogmatic Theology led him to the conclusion of a close link between doctrinal differences and historical developments. Thus, in his later years, he concentrated on historical research, mostly of the Middle Ages but also of the 18th and 19th centuries.