By far the major point of Paul’s argumentation about the change that Christ brings is Post Millennialism. The downward spiral of Israel and the Nations that could not be stopped because of sin working in the flesh has now been stopped and overcome. Christ now brings a reign of grace in the place of the reign of death. Where once sin reigned in the members of our body now we have the resurrection of Christ in history to empower and guarantee that we can serve righteousness.
This change is paradoxical because it continues to come about through the way of the cross. The Spirit groans within us because we don’t see it happening as it should, but those groanings are birth pangs.
But the point is that now, at last, the obedience of faith among the nations is possible. It can be done whereas before it was doomed.
PostMillennialism. Without it much of Romans will make no sense.