I. He suspends his opinion on the appointment of Anatolius till he has made open confession of the Catholic Faith.
In all your piously expressed letters amid the anxieties, which we suffer for the Faith, you have afforded us hope of security by supporting the Council of Nicæa so loyally as not to allow the priests of the Lord to budge from it, as you have often written us already. But lest I should seem to have done anything prejudicial to the Catholic defence, I thought nothing rash on either side ought meanwhile to be written back on the ordination of him who has begun to preside over the church of Constantinople, and this not through want of loving interest, but waiting for the Catholic Truth to be made clear.
And I beg your clemency to bear this with equanimity that when he has proved himself such as we desire towards the Catholic Faith, we may the more fully and safely rejoice over his sincerity. But that no evil suspicion may assail him about our disposition towards him, I remove all occasion of difficulty, and demand nothing which may seem either hard or controvertible but make an invitation which no Catholic would decline. For they are well known and renowned throughout the world, who before our time have shone in preaching the Catholic Truth whether in the Greek or the Latin tongue, to whose learning and teaching some even of our own day have recourse, and from whose writings a uniform and manifold statement of doctrine is produced: which, as it has pulled down the heresy of Nestorius, so has it cut off this error too which is now sprouting out again.
Let him then read again what is the belief on the Lord's Incarnation which the holy fathers guarded and has always been similarly preached, and when he has perceived that the letter of Cyril of holy memory, bishop of Alexandria, agrees with the view of those who preceded him [wherein he wished to correct and cure Nestorius, refuting his wrong statements and setting out more clearly the Faith as defined at Nicæa, and which was sent by him and placed in the library of the Apostolic See], let him further reconsider the proceedings of the Ephesian Synod wherein the testimonies of Catholic priests on the Lord's Incarnation are inserted and maintained by Cyril of holy memory.
Let him not scorn also to read my letter over, which he will find to agree throughout with the pious belief of the fathers. And when he has realized that that is required and desired from him which shall serve the same good end, let him give his hearty assent to the judgment of the Catholics, so that in the presence of all the clergy and the whole people he may without any reservation declare his sincere acknowledgment of the common Faith, to be communicated to the Apostolic See and all the Lord's priests and churches, and thus the world being at peace through the one Faith, we may all be able to say what the angels sang at the Saviour's birth of the Virgin Mary, “Glory in the highest to God and on earth peace to men of good will.”
Source: Letters (New Advent)