Grace reigns in the lives of the redeemed children of God on earth. In Romans 5:21 Paul is highlighting what a special time the Roman Christians lived in, namely during the inauguration of the new dispensation of our Lord. Prior to the incarnation of Jesus, sin and death reigned. Now another kingdom is inaugurated—one wherein grace also might reign through righteousness leading to eternal life through Jesus Christ our Lord.
By emphasising the special bond between us (the many) and the One (our Lord), Paul shows that he did not propose an impersonal, universal reconciliation in this passage (Romans 5:11–21). The gospel does, however, proclaim one universal Redeemer. This is sufficient for us who can now be content with not knowing the nature of God's final judgment over the nations.
God’s sovereign plan for the world, in which the seemingly all-powerful reign of sin is ultimately defeated by the reign of grace through righteousness, culminates in the one God-man: Jesus Christ our Lord.
Paul did not use the phrase our Lord
at all in the preceding passage (Romans 5:12–20), but in now leads us back to the point he was making in Romans 5:11: through him, our Lord, we who were under the reign of death, have now been reconciled with the living God.1
21 so that, as sin reigned in death, grace also might reign through righteousness leading to eternal life through Jesus Christ our Lord.