IV. Those who undertake to speak authoritatively on doctrine, must preserve the balance between the extremes.
Accordingly while he strove to cut short Flavian of blessed memory's life in the present world, he has deprived himself of the light of true life. While he tried to drive you out of your churches, he has cut off himself from fellowship with Christians. While he drags and drives many into agreement with error, he has stabbed his own soul with many a wound, a solitary convicted offender beyond all, and through all and for all, for he was the cause of all men's being accused. But, although, brother, you who are nurtured on solid food, have little need of such reminders, yet that we may fulfil what belongs to our position according to that utterance of the Apostle who says, “Besides these things that are without, that which presses on me daily, anxiety for all the churches.
Who is weakened and I am not weak? Who is made to stumble and I burn not?” we believe this admonition ought to be given especially on the present occasion, that whenever by the ministration of the Divine grace we either overwhelm or cleanse those who are without, in the pool of doctrine, we go not away in anything from those rules of Faith which the Godhead of the Holy Ghost brought forward at the Council of Chalcedon, and weigh our words with every caution so as to avoid the two extremes of new false doctrine: not any longer (God forbid it) as if debating what is doubtful, but with full authority laying down conclusions already arrived at; for in the letter which we issued from the Apostolic See, and which has been ratified by the assent of the entire holy Synod, we know that so many divinely authorised witnesses are brought together, that no one can entertain any further doubt, except one who prefers to enwrap himself in the clouds of error, and the proceedings of the Synod whether those in which we read the formulating of the definition of Faith, or those in which the aforesaid letter of the Apostolic See was zealously supported by you, brother, and especially the address of the whole Council to our most religious Princes, are corroborated by the testimonies of so many fathers in the past that they must persuade any one, however unwise and stubborn his heart, so long as he be not already joined with the devil in damnation for his wickedness.
Source: Letters (New Advent)