5 As to whether there is anything objectionable about the conversation of Paulinus, you can say yourselves. What distresses me is that he should show an inclination for the doctrine of Marcellus, and unreservedly admit his followers to communion. You know, most honourable brethren, that the reversal of all our hope is involved in the doctrine of Marcellus, for it does not confess the Son in His proper hypostasis, but represents Him as having been sent forth, and as having again returned to Him from Whom He came; neither does it admit that the Paraclete has His own subsistence.
It follows that no one could be wrong in declaring this heresy to be all at variance with Christianity, and in styling it a corrupt Judaism. Of these things I implore you to take due heed. This will be the case if you will consent to write to all the Churches of the East that those who have perverted these doctrines are in communion with you, if they amend; but that if they contentiously determine to abide by their innovations, you are separated from them. I am myself well aware, that it had been fitting for me to treat of these matters, sitting in synod with you in common deliberation.
But this the time does not allow. Delay is dangerous, for the mischief they have caused has taken root. I have therefore been constrained to dispatch these brethren, that you may learn from them all that has been omitted in my letter, and that they may rouse you to afford the succour which we pray for to the Churches of the East.
Source: Letters (New Advent)