Tertullian, Against Marcion 14
If the Father sent him in the likeness of sinful flesh, then the flesh visible in him will not be called a phantom on that account. He had assigned sin to the flesh in the first place and turned it into a law of sin dwelling in its members and opposing the law of the mind. That is why the Son was sent in the likeness of sinful flesh: to redeem sin's flesh with a matching substance—that is, with flesh resembling sinful flesh while itself not being sinful. This will be God's power: to accomplish salvation in a substance that is the counterpart. It is no great thing if the Spirit of God were to heal flesh; the wonder is if flesh, akin to sinful flesh, while still being flesh, is not of sin. So the likeness attaches to the label 'sin', not to a falsity of substance. He would not have added 'of sin' if he had wanted the likeness of substance to be understood so as to deny the truth; he would have said only 'flesh', not also 'of sin'. But when he framed it as 'flesh of sin', he confirmed the substance—that is, the flesh—and referred the likeness to the vice of the substance, that is, to sin. Suppose the likeness of substance is what is spoken of: the truth of the substance is not thereby denied. Why then is it similar if it is true? Because it is indeed true, but not from seed; it is similar and true in condition, but not similar in origin. Besides, there is no likeness between opposites. The Spirit would not be called the likeness of flesh—since flesh would not take on the likeness of Spirit—but it would be called a phantom if what does not exist were seen. Likeness is spoken of when there is something actually seen, because it exists while matching another. A phantom, merely by being that, is not a likeness. Here too he himself, explaining how he does not want us to be in the flesh while we are in the flesh, so that we may not be in the works of the flesh, shows that he wrote for this reason: 'flesh and blood will not inherit the kingdom of God' (1 Corinthians 15:50), not condemning the substance but its works; which, because they can be rejected by us while we remain in the flesh, belong not to the guilt of the substance but to our conduct.
Latin
Hunc si pater misit in similitudinem carnis peccati, non ideo phantasma dicetur caro, quae in illo uidebatur. peccatum enim carni supra adscripsit et illam fecit legem peccati habitantem in membris suis et aduersantem legi sensus. ob hoc igitur missum filium in similitudinem carnis peccati, ut peccati carnem simili substantia redimeret, id est carne, quae peccatrici carni similis esset, cum peccatrix ipsa non esset. nam et haec erit dei uirtus in substantia pari perficere salutem. non enim magnum, si spiritus dei carnem remediaret, sed si caro, consimilis peccatrici, dum caro est, sed non peccati. ita similitudo ad titulum peccati pertinebit, non ad substantiae mendacium. nam nec addidisset 'peccati', si substantiae similitudinem uellet intellegi, ut negaret ueritatem; tantum enim (carnis) posuisset, non et (peccat ? . cum uero tunc sic struxit: 'carnis peccati', et substantiam confirmauit, id est carnem, et similitudinem ad uitium substantiae retulit, id est ad peccatum. puta nunc similitudinem substantiae dictam: non ideo negabitur substantiae ueritas. (cur ergo similis, (si) uera'? quia uera quidem, sed non ex semine: de statu similis et uera, de censu non uero dissimilis. ceterum similitudo in contrariis nulla est. spiritus non diceretur carnis similitudo, — quia nec caro similitudinem spiritus caperet — sed phantasma diceretur, si id quod non erat uidebatur. similitudo autem dicitur, cum est quod uidetur. est enim, dum alterius par est. phantasma autem, qua hoc tantum est, non est similitudo. Et hic autem ipse edisserens, quomodo nolit nos esse in carne, cum simus in carne, ut scilicet non simus in operibus carnis, ostendit hac ratione scripsisse: caro et sanguis regnum dei non consequentur, non substantiam damnans, sed opera eius; quae, (quia) possunt non admitti a nobis in carne adhuc positis, non ad reatum substantiae, sed ad conuersationispertinebunt.