Then he appeals to the authority of the Ecclesiastical Synods against the Irish usage. There was, he admits, in the beginning a diversity of practice even in the Apostolic churches founded by Peter the Key-bearer, and John the Eagle-pinioned, for the Apostles themselves, driven hither and thither by persecution, had no time to fix a uniform cycle for all the Churches. But afterwards "I find it was ordered that all those were to be excommunicated who dared to act against the statutes of the four Apostolic Sees of Rome, Jerusalem, Antioch, and Alexandria." The Nicene Synod, he adds, composed of three hundred and eighteen bishops, ordained that the same rule should be followed in all the Churches of the East and West. The Synod of Arles also, where six hundred bishops were present, insisted on uniformity throughout the whole world in the observance of the Pasch, lest, as St. Jerome observes, we should run the risk of eating the Pasch contrary to the law, _extra unam domum_, that is, outside the communion of the Universal Church. "Consider you well, therefore, whether it is the Hebrews, Greeks, Latins, and Egyptians, united together, that are the _extra domum_, or a fragment of the Scots and Britains, living at the end of the world, that form a conventicle separated from the communion of the Church. You are the leaders of the people; beware how you act, leading others into error by your obstinacy. Not so our Fathers, whom you pretend to follow, for they were blameless in their own days, seeing that they faithfully followed what they thought in their simplicity to be best; but you can scarcely excuse yourselves for knowingly rejecting the observances of the Universal Church." The writer then proceeds to insist at great length on this argument from the practice and authority of the Church; and recites various passages from St. Augustine, St. Jerome, St. Cyprian, and St. Gregory, on the unity of the Church, and the guilt and danger of schismatical practices. "Non alia Romanae urbis ecclesia, alia totius orbis aestimanda est," he says, quoting St. Augustine; and then he adds from St. Jerome, "Si quis Cathedrae S. Petri jungatur meus est ille,"--communion with Rome was in Cummian's estimation, as in Jerome's, the test of orthodoxy both in doctrine and discipline. "Can anything," he says, "be more absurd than to say of our mother the Church--Rome errs, Jerusalem errs, Antioch errs, and the whole world errs, the Irish (Scoti) and Britons alone are in the right?" In this part of his letter Cummian certainly displays not only great learning, but also great vigour and eloquence of style.