Archpriest John Romanidis stood at the origins of the return of modern Greek theology to patristic roots and in this sense was considered the successor of Fr. Georgy Florovsky, who was his teacher at Harvard University. One of the most important aspects of the theology of Fr. John was the purity and evangelical-patristic authenticity of Orthodox theology, mainly in comparison with the deviations from it that occurred in the West. In particular, Fr. John, with truly patristic depth, refuted the triadological errors that arose in the Western Church as a result of the spread of the Filioque.