Novatian, On the Trinity 23
At this point I am free to collect arguments even from other heretical groups. Proof drawn from an opponent is especially firm, because it lets the truth be confirmed by the very enemies of truth themselves. Scripture makes it so clear that God exists that many heretics, overwhelmed by the magnitude and truth of the divine nature, have pushed their honors for him beyond all measure. They have gone so far as to proclaim not the Son but God the Father himself. Although this runs contrary to scriptural truth, it still stands as a great and principal argument for the divinity of Christ. He is so fully God, yet precisely as the Son of God born from God, that many heretics have accepted him as God in such a way that they thought he must be not the Son but the Father.
Let them consider, then, whether this one is God, whose authority has so moved certain people that they came to regard him as God the Father himself, as we noted earlier. They confessed the divinity in Christ without restraint and with abundant zeal, driven by the manifest divinity of Christ to think him the Father, because they perceived him to be God, the very one they read about as the Son. Other heretics have so embraced the manifest divinity of Christ that they declared he was without flesh, stripping away the whole man he assumed. They did this lest they diminish the power of the divine name in him, supposing that associating a human birth with him would weaken it. We do not approve of that view, but we do advance the argument that Christ is so fully God that some, once the man was removed, thought him to be only God, while others believed him to be God the Father himself.
The reason and balance of the heavenly scriptures show Christ to be God, but as the Son of God, and with the man assumed by God and also the Son, he is to be believed as a man as well. Because he came to humanity in order to be the mediator of God and men, he had to be one with humanity, and the Word had to become flesh. Only so could he establish harmony in himself between earthly and heavenly realities, binding the pledges of both sides in his own person and joining God to man and man to God. As a result, the Son of God, by assuming flesh, becomes the Son of man, and the Son of man, by receiving the Word of God, becomes the Son of God. The salvation of the human race, destined before the ages, finds its fulfillment in the Lord Jesus Christ, who is both God and man, and by this condition the human race is led to the fruit of eternal salvation.
Latin
Hoc in loco licebit mihi argumenta etiam ex aliorum haereticorum parte conquirere. firmum est genus probationis, quod etiam ab aduersario sumitur, ut ueritas etiam ab ipsis inimicis ueritatis probetur. nam usque adeo hunc manifestum est in scripturis esse et deum tradi, ut plerique haereticorum, diuinitatis ipsius magnitudine et ueritate commoti, ultra modum extendentes honores eius, ausi sint non filium sed ipsum deum patrem promere uel putare. quod, etsi contra scripturarum ueritatem est, tamen diuinitatis Christi argumentum grande atque praecipuum est; qui usque adeo deus, sed qua filius dei natus ex deo, ut plerique illum (ut diximus) haeretici ita deum acceperint, ut non filium sed patrem pronuntiandum putarint. aestiment ergo an hic sit deus, cuius auctoritas tantum mouit quosdam, ut putarent illum, ut diximus superius, iam ipsum patrem deum, effrenatius et -effusius in Christo diuinitatem confitentes, ad hoc illos manifesta Christi diuinitate cogente, ut, quem filium legerent, quia deum animaduerterent, patrem putarent. alii quoque haeretici usque adeo Christi manifestam amplexati sunt diuinitatem, ut dixerint illum fuisse sine carne, et totum illi susceptum detraxerint hominem, ne decoquerent in illo diuini nominis potestatem, si humanam illi sociassent, ut arbitrabantur, natiuitatem. quod tamen nos non probamus; sed argumentum afferimus usque adeo Christum esse deum, ut quidam illum, subtracto homine, tantummodo putarint deum, quidam autem ipsum crediderint patrem deum: cum ratio et temperamentum scripturarum caelestium Christum ostendant deum, sed qua filium dei, et, assumpto a deo etiam filio hominis, credendum et hominem. quoniam si ad hominem ueniebat, ut mediator dei et hominum esse deberet, oportuit illum cum eo esse, et uerbum carnem fieri, ut in semetipso concordiam confibularet terrenorum pariter atque caelestium, dum utriusque partis in se conectens pignora et deum homini et hominem deo copularet; ut merito filius dei per assumptionem carnis filius hominis, et filius hominis per receptionem dei uerbi filius dei effici possit. salutem generis humani ante saecula destinatum, in domino Iesu Christo deo et homine inuenitur impleri, quo condicio generis humani ad fructum aeternae salutis posset adduci.