III. He sends a letter of St. Athanasius to show that the present heresy is only a revival of former exploded heresies.
But lest the instruction necessary for the confirmation of faithful spirits or the refutation of heretics should be wanting or not expressed, I have sent the letter of bishop Athanasius of holy memory addressed to bishop Epictetus, whose testimony Cyril of holy memory made use of at the Synod of Ephesus against Nestorius, because it has so clearly and carefully set forth the Incarnation of the Word, as to overthrow both Nestorius and Eutyches by anticipation in the heresies of those times.
Let the followers of Eutyches and Dioscorus dare to accuse such an authority as this of ignorance or of heresy, who assert that our preaching goes astray from the teaching and the knowledge of the Fathers. But it ought to avail for the confirmation of the minds of all the Lord's priests, who, having been already detected and condemned of heresy in respect of the authorities they followed, now begin more openly to set forth their blasphemous dogma, lest, if their meaning were hid beneath the cloke of silence it might still be doubtful whether the triple error of Apollinaris, and the mad notion of the Manichees was really revived in them.
And as they no longer seek to hide themselves but rise boldly against the churches of Christ, must we not take care to destroy all the strength of their attempts, observing, as I have said, such discrimination as to separate the incorrigible from the more docile spirits: for “evil conversations corrupt good manners,” and “the wise man will be sharper than the pestilent person who is chastised;” in order that in whatever way the society of the wicked is broken up, some vessels may be snatched from the devil's hand? For we ought not to be so offended at scurrilous and empty words as to have no care for their correction.
Source: Letters (New Advent)