He also became engaged in a controversy with John the Faster, the Patriarch of Constantinople, about the title of "Universal Bishop," which was arrogated to the latter by himself and those about him. It was not a novelty, but Gregory seems to have seen the danger involved in its continued usage to the power which he claimed for the See of Rome. A whole series of his letters are consequently taken up with his vehement, not to say violent, protests against John's use of the title. It is probably in connection with the fact that the Emperor Maurice had supported the Patriarch John in his claim of equality with the Pope of Rome, that the explanation is to be sought of a circumstance which remains the chief blot on Gregory's fame. Maurice had given him little help against the Lombards, and had in various ways seemed to oppose or actually opposed Gregory in some of his reforms. When, therefore, Phocas murdered Maurice and usurped his throne, the Pope wrote him a fulsome letter of congratulation. He may not have been fully acquainted with the infamous character of Phocas, nor have fully known of the atrocious manner in which he had murdered the Emperor and his family, yet he must have known, at least, that he was a traitor, a murderer, and an usurper. Nothing can excuse him--knowing this--for writing in such a strain, saying "Glory to God in the highest," and "Let the heavens rejoice and let the earth be glad," at the hopes aroused by the piety of the new Emperor. He attached great importance to preaching, and many of his sermons remain to this day. He also wrote "Liber Pastoralis Curæ," a treatise on the responsibilities and duties of Bishops. This book had immense influence; it was circulated in Spain; the Emperor had it translated into Greek; it was an authoritative text-book in Gaul for centuries; and it was translated into Anglo-Saxon by King Alfred, and was widely disseminated in England. But it is in the services and service-books of the Church that he set his mark most conspicuously. He organized and enriched them, even the Canon of the Mass in which he added to the prayer of oblation the words "Diesque nostras in tua pace disponas." The work which has been traditionally ascribed to him in the department of Church Music we shall enter into more fully.