14 For as to what some say, as if it tended to favour heretics, that the Apostle Paul declared, “Only every way, whether in pretence or in truth, let Christ be preached,” we find that this also can avail nothing to their benefit who support and applaud heretics. For Paul, in his epistle, was not speaking of heretics, nor of their baptism, so that anything can be shown to have been alleged which pertained to this matter. He was speaking of brethren, whether as walking disorderly and against the discipline of the Church, or as keeping the truth of the Gospel with the fear of God.
And he said that certain of them spoke the word of God with constancy and courage, but some acted in envy and dissension; that some maintained towards him a benevolent love, but that some indulged a malevolent spirit of dissension; but yet that he bore all patiently, so long only as, whether in truth or in pretence, the name of Christ which Paul preached might come to the knowledge of many; and the sowing of the word, which as yet had been new and irregular, might increase through the preaching of the speakers.
Besides, it is one thing for those who are within the Church to speak concerning the name of Christ; it is another for those who are without, and act in opposition to the Church, to baptize in the name of Christ. Wherefore, let not those who favour heretics put forward what Paul spoke concerning brethren, but let them show if he thought anything was to be conceded to the heretic, or if he approved of their faith or baptism, or if he appointed that perfidious and blasphemous men could receive remission of their sins outside the Church.
Source: The Epistles of Cyprian (New Advent)