His greatness was not only due to his defense of Orthodoxy against heretical papal practices, but also connected to his love and meekness. He vigorously opposed the addition of the filioque clause to the Nicene - Constantinopolitan Creed, and wrote On the Mystagogy of the Holy Spirit to preserve "the purity of our religion" and to hinder "those who chose to promote any other definition of dogma than the unanimous and common faith of the pious". 
      St. Photios was forced to become Patriarch of Constantinople, however he took his calling seriously and at once set to work as a man of God..  One of his activities was to correct the error of Pope Nicholas of Rome who enslaved the people of the West with threats of condemnation to hell for disobedience to the pope. Holy Photios wrote to Nicholas, "Nothing is dearer that the Truth."  In the same letter he noted, "It is truly necessary that we observe all things, but above all, that which pertains to matters of Faith, in which but a small deviation represents a deadly sin."