Against Marcion 1.21

Besides, if, in preaching a new god, he wished to exclude the law of the old God, why does he lay down nothing about the new god but only about the old law — unless because, while faith in the Creator remained, only his law was to cease? As that psalm had sung beforehand: “Let us break their bonds from us and cast away their yoke from us” — from the time, that is, when “the nations raged and the peoples meditated vain things; the kings of the earth stood up, and the rulers gathered together against the Lord and against his Christ.” And surely, if another god were being preached by Paul, there would be no dispute whether the law was to be kept or not, since it would not belong to the new lord, the rival of the law. For the very newness and difference of the god would have removed not only the question of an old and alien law but all mention of it. But this was the whole state of the question: how, when the same God of the law was being preached in Christ, his law could be set aside. Faith, then, always stood firm in the Creator and his Christ, but conduct and discipline wavered. For some disputed about eating what had been sacrificed to idols, others about the veiling of women, others about marriages and divorces, some even about the hope of the resurrection; about God, no one. For if this question too had been disputed, it would also be found in the apostle, and all the more as the principal question.

But if after the times of the apostles the truth suffered adulteration concerning the rule of God, then the apostolic tradition in its own time suffered none concerning the rule of God; and no other tradition of the apostles is to be acknowledged than that which is set forth today in their own churches. But you will find no church of apostolic stock that is not Christian in the Creator. Or if these are to have been corrupt from the beginning, which will be sound? The Creator's opponents, no doubt! Produce, then, one of your churches of apostolic stock, and you will have carried the case. Since, then, it is established in every way that there was no other god in the rule of this sacred pledge from Christ down to Marcion than the Creator, our proof is now sufficiently fortified, by which we have shown that knowledge of the heretical god began from the separation of gospel and law; and the earlier definition is also supported, that no god is to be believed whom a man has composed from his own mind — unless, plainly, he is a prophet, that is, one who does not speak from his own mind. If Marcion can be called that, it will also have to be proved … there will be no need to discuss it further. For with this wedge of truth every heresy is driven out, once Christ is shown to be the bearer of no other god than the Creator.