" Whose grace, if not of that God from whom also came the law? Unless it be, forsooth, that the Creator intercalated His law for the mere purpose of producing some employment for the grace of a rival god, an enemy to Himself (I had almost said, a god unknown to Him), "that as sin had" in His own dispensation "reigned unto death, even so might grace reign through righteousness unto (eternal) life by Jesus Christ," His own antagonist! For this (I suppose it was, that) the law of the Creator had "concluded all under sin," and had brought in "all the world as guilty (before God)," and had "stopped every mouth," so that none could glory through it, in order that grace might be maintained to the glory of the Christ, not of the Creator, but of Marcion! I may here anticipate a remark about the substance of Christ, in the prospect of a question which will now turn up.
" By a figure we die in our baptism, but in a reality we rise again in the flesh, even as Christ did, "that, as sin has reigned in death, so also grace might reign through righteousness unto life eternal, through Jesus Christ our Lord." But how so, unless equally in the flesh? For where the death is, there too must be the life after the death, because also the life was first there, where the death subsequently was.
Paul shows that there are two kingdoms in man. In one of these, sin has taken control and leads to death. In the other, grace reigns through righteousness and leads to life. For it is grace which expels and ejects sin from its kingdom, i.e., from our members.
This he says to show that the latter ranks as a king, the former, death, as a soldier, being marshalled under the latter, and armed by it. If then the latter (i.e. sin) armed death, it is plain enough that the righteousness destructive hereof, which by grace was introduced, not only disarms death, but even destroys it, and undoes entirely the dominion thereof, in that it is the greatest of the two, as being brought in not by man and the devil, but by God and grace, and leading our life unto a goodlier estate, and to blessings unlimited. For of it there will never be any end (to give you a view of its superiority from this also). For the other cast us out of our present life, but grace, when it came, gave us not the present life, but the immortal and eternal one. But for all these things Christ is our voucher. Doubt not then for your life if you have righteousness, for righteousness is greater than life as being mother of it.
Just as the reign of sin was established through contempt for the law, so also the reign of grace is established through the forgiveness of many sinners and thereafter through the doing of righteousness without ceasing.
Paul says that just as sin once ruled us even against our will, because we were so used to it, so now our zeal for God reigns and will reign in us forever. Since we have been made worthy of eternal life through the resurrection and live in true and certain righteousness, we shall no longer be receptive to sin.
[AD 220] Tertullian on Romans 5:21