Tertullian, Against Marcion 5.10

Let us return now to the resurrection. We have already answered every heretic on this point in a dedicated volume, yet we do not drop the matter here, for the sake of those who have never seen that little work. "What will those do who are baptized for the dead, if the dead do not rise?" (1 Corinthians 15:29). Let that practice answer for itself: perhaps the Kalends of February will speak up for those who ask on behalf of the dead. So do not make the apostle the author or guarantor of this rite, as if he invoked it to prop up the resurrection of the flesh — implying that people baptize for the dead in vain, driven by faith in that resurrection. We have him somewhere defining a single baptism. Therefore, to be baptized for the dead is to be baptized for bodies — for we have shown the body is dead — and so the question stands: what will those do who are baptized for bodies, if bodies do not rise? We plant this step firmly, so that the apostle's second argument also deals equally with the body. Some will ask, "How are the dead raised? With what kind of body do they come?" Once the resurrection — which was being denied — had been defended, it followed naturally to discuss the quality of the body, which was not yet seen. But it is proper to take up that topic with others. For Marcion, who refuses the resurrection of the flesh altogether and promises salvation only to the soul, raises a question not of quality but of substance.