Tertullian — Against Marcion 14

If the Father sent His Son in the likeness of sinful flesh, Romans 8:3 it must not therefore be said that the flesh which He seemed to have was but a phantom. For he in a previous verse ascribed sin to the flesh, and made it out to be the law of sin dwelling in his members, and warring against the law of the mind. On this account, therefore, (does he mean to say that) the Son was sent in the likeness of sinful flesh, that He might redeem this sinful flesh by a like substance, even a fleshly one, which bare a resemblance to sinful flesh, although it was itself free from sin . Now this will be the very perfection of divine power to effect the salvation (of man) in a nature like his own.

For it would be no great matter if the Spirit of God remedied the flesh; but when a flesh, which is the very copy of the sinning substance — itself flesh also — only without sin , (effects the remedy, then doubtless it is a great thing). The likeness , therefore, will have reference to the quality of the sinfulness, and not to any falsity of the substance. Because he would not have added the attribute sinful, if he meant the likeness to be so predicated of the substance as to deny the verity thereof; in that case he would only have used the word flesh, and omitted the sinful. But inasmuch as he has put the two together, and said sinful flesh, (or flesh of sin , ) he has both affirmed the substance, that is, the flesh and referred the likeness to the fault of the substance, that is, to its sin .

But even suppose that the likeness was predicated of the substance, the truth of the said substance will not be thereby denied. Why then call the true substance like ? Because it is indeed true , only not of a seed of like condition with our own; but true still, as being of a nature not really unlike ours. And again, in contrary things there is no likeness. Thus the likeness of flesh would not be called spirit , because flesh is not susceptible of any likeness to spirit; but it would be called phantom , if it seemed to be that which it really was not. It is, however, called likeness , since it is what it seems to be. Now it is (what it seems to be), because it is on a par with the other thing (with which it is compared). But a phantom, which is merely such and nothing else, is not a likeness.

The apostle, however, himself here comes to our aid; for , while explaining in what sense he would not have us live in the flesh, although in the flesh — even by not living in the works of the flesh — he shows that when he wrote the words, Flesh and blood cannot inherit the kingdom of God , 1 Corinthians 15:50 it was not with the view of condemning the substance (of the flesh), but the works thereof; and because it is possible for these not to be committed by us while we are still in the flesh, they will therefore be properly chargeable, not on the substance of the flesh, but on its conduct.