7 [The fair thing would be to judge of me, not from one or two who do not walk uprightly in the truth, but from the multitude of bishops throughout the world, connected with me by the grace of the Lord. Make enquiries of Pisidians, Lycaonians, Isaurians, Phrygians of both provinces, Armenians your neighbours, Macedonians, Achæans, Illyrians, Gauls, Spaniards, the whole of Italy, Sicilians, Africans, the healthy part of Egypt, whatever is left of Syria; all of whom send letters to me, and in turn receive them from me.] From these letters, alike from all which are dispatched from them. and from all which go out from us to them, you may learn that we are all of one mind, and of one opinion. [Whoso shuns communion with me, it cannot escape your accuracy, cuts himself off from the whole Church.
Look round about, brethren, with whom do you hold communion? If you will not receive it from me, who remains to acknowledge you? Do not reduce me to the necessity of counselling anything unpleasant concerning a Church so dear to me.] There are things now which I hide in the bottom of my heart, in secret groaning over and bewailing the evil days in which we live, in that the greatest Churches which have long been united to one another in brotherly love, now, without any reason, are in mutual opposition.
Do not, oh! Do not, drive me to complain of these things to all who are in communion with me. Do not force me to give utterance to words which hitherto I have kept in check by reflection and have hidden in my heart. Better were it for me to be removed and the Churches to be at one, than that God's people should suffer such evil through our childish ill-will. [Ask your fathers, and they will tell you that though our districts were divided in position, yet in mind they were one, and were governed by one sentiment. Intercourse of the people was frequent; frequent the visits of the clergy; the pastors, too, had such mutual affection, that each used the other as teacher and guide in things pertaining to the Lord.]
Source: Letters (New Advent)