I. Eutyches is now clearly seen to have deviated from the Faith.
Your letter, beloved, which has just reached me, shows with what spiritual love of the Catholic Faith you are inspired: and it makes me very glad that devout hearts all agree in the same opinion, so that according to the teaching of the Holy Ghost there may be fulfilled in us what the Apostle says: “Now I beseech you, brethren, through the name of our Lord Jesus Christ, that you all speak the same things, and there be no divisions among you: but that you be perfect in the same mind and in the same judgment.”
But Eutyches has put himself quite outside this unity, if he perseveres in his perversity, and still does not understand the bonds with which the devil has bound him, and thinks any one is to be reckoned among the Lord's priests, who is a party to his ignorance and madness. For some time we were uncertain in what he was displeasing to Catholics: and when we received no letter from our brother Flavian, and Eutyches himself complained in his letter that the Nestorian heresy was being revived, we could not fully learn the source or the motive of so crafty an accusation. But as soon as the minutes of the bishops' proceedings reached us, all those things which were hidden beneath the veil of his deceitful complaints were revealed in their abomination.
Source: Letters (New Advent)