The meaning is that, if Christ died for all, it was because all had died: otherwise there would have been no such need for Him to die. You need not go down into a pit where one will perish, if he is not there perishing. That it is not all died to sin is evident from the correspondency of "all" in the sentence; and further that "they which live" are taken as some out of the "all" in what follows. "He died for all, that they which live should not henceforth live," etc.—οἱ ζῶντες, not ζῶντες. Hence he does not know even Christ after the flesh, as a living Jewish Messiah, whom as a Jew he would have known: "God was in Christ, reconciling the world." Nor does he know Christians as belonging to the old, creation to which they had died, nor others, for they were all dead—their whole history. But if a man was in Christ, it was a new creation: he belonged to that in which all things were of God.
The whole subject is the power of life in Christ as triumphant over death. Hence, when he applies it, he does not say merely "who died for them," as when he speaks of all, but "rose again" also. It is the power and fullness of a new thing for those taken out of death through Christ's going down into it. There was neither Jew, Gentile, sin, flesh, nor any other thing of the old Adam or legal estate, but a new creation.
[1869.]