Dionysius Exiguus, Ep. ad Petronium (Krusch, Studien 2: 66)
and anathematized who go against the canonical statutes of the fourfold Apostolic See, namely that of Rome, Jerusalem, Antioch and Alexandria, which agree on the unity of Easter. Added to these was the Synod of Nicaea of 318 bishops, who decreed that the ancient canon concerning the observation of Easter [should be observed] through which in future no disagreement would arise among the churches, with all things rightly disposed, and one and the same peace and faith of the churches would be maintained in Eastern and Western partsSynodus Niceae, Canon 1, apud Rufinum, Hist. Eccl. 10: 6 (Hefele-Leclercq, Hist. des conciles 1/2: 1175)
Again, in the Synod of Arles of 600 bishops, which first of all [confirmedSynodus Arelatensis, Canon 1 (CCSL 148: 9)
so that the universal Church, according to the Apostle, might honour [the one] God with one voice.Rom. 15:6
Whence care should be taken, as Jerome says, lest we eat the figural lamb outside of the one house against the precept of the Law, that is outside of the universal Church. From which it is manifest, he says, that Jews and heretics and all conventicles of perverse doctrines who do not eat the Lamb in the one Church do not eat the flesh of the Lamb, but that of the dragon that was given, according to the Psalter, as food to the Ethiopian people.Ps. 73:14
And this I fear. But you ought to consider which are the conventicles of which I spoke, whether they are the Hebrews, Greeks, Latins and Egyptians who are united in their observance of the principal solemnities, or an insignificantMatt. 7:2
and this is the danger hanging over you. For you are the heads and the eyes of the people, and if they are led into error because of your obstinacy you shall answer,Exod. 34:33; 2 Cor. 3:13
according to Ezechiel, for the blood of [each] soulEzek. 33:6 and 8
to the strict Judge. Our elders, however, whom you hold as a cloak for your rejection, kept simply and faithfully, without blame of any contradiction or animosity, that which they knew to be best in their day, and prescribed for their posterity thus, according to the Apostle: Test everything, hold fast what is good, abstain from every form of evil.1 Thess. 5:21-22
But I fear lest it happen that you should judge the unanimous rule of the Catholic Church to be a form of evil, which heaven forbid!