To John, Bishop.
Gregory to John, Bishop of Constantinople.
As the pravity of heretics is to be repressed by the zeal of a right faith, so the integrity of a true confession is to be embraced. For, if one who declares himself sound in the faith is scorned, the faith of all is brought into doubt, and fatal errors are generated from inconsiderate strictness. And hence not only are wandering sheep not recalled to their Lord's folds, but even those that are within them are exposed to be cruelly torn by the teeth of wild beasts. Let us then fully consider this, most dear brother, and not suffer any one who truly professes the Catholic faith to be distressed under pretext of heresy, nor (which God forbid) allow heresy to grow the more under show of correcting it.
But we have wondered much why those who were deputed by you as judges in a matter of faith against John, presbyter of the church of Chalcedon, believed report, disregarding truth, and would not believe him when he distinct professed his faith; especially as his accusers, when asked what was the heresy of the Marcionists which they spoke of, and on the ground of which they endeavoured to make him out guilty, replied by a plain confession that they did not know. From which circumstance it evidently comes out that, without regard to God, not justly, but against their own souls, they were desirous only of injuring him personally of their own mere will. We therefore, after Council held (as the tenor of the proceedings before us shows), having thoroughly examined and considered all that was necessary. inasmuch as we have been unable to find the aforesaid presbyter in any respect guilty, and especially as the plea which he delivered to the judges delegated by you is in entire accordance with the integrity of a right faith, we I say on this account, disapproving the sentence of the said judges, through the revealing grace of Christ our God and Redeemer, pronounce him by our definite sentence Catholic and free from all charge of heresy. Seeing, then, that we have sent him back to your Holiness, it is for you to receive him with the kindness which you show to all, and bestow on him your priestly charity, and defend him from all molestation, nor allow any one to busy himself in causing him trouble: but, as you defend others from oppression, so from him ought you not to withhold your succour.
Source: Register of Letters (New Advent)