The eschatological life of the believer requires the legal restitution of sin’s guilt by means of an imputed righteousness for justification—a kingdom benefit received only in union with Christ by his Spirit through faith. While Paul spoke of the death of Christ in Romans 1:3-4 and its application for salvation to all who believe in 1:16-17, now in 5:1-11 he expounds its substitutionary nature, having just declared Abraham justified before God on account of the righteousness he received not by works of the law, but through faith. Christ did not die for his own sin, but for us while we were helpless (v. 6), sinners (v. 8), and enemies (v. 10). The death of Christ established peace with God (5:1) for by it we were reconciled to God (5:10)—both forensic terms in keeping with justification.
Vos, commenting on Romans 5:9-11, states, “The objective reconciliation took place in the death of Christ; its subjective result is justification. … The two are entirely equivalent. … [Reconciliation] consisted in the removal of objective legal obstacles…. According to Romans … the two transactions of reconciliation and justification are in substance identical. They both rest on the death, or the blood, of Christ.”
Ridderbos gets at the eschatological thrust of reconciliation by defining it as “the work of redemption going out from God in Christ to the world, for the removal of ‘enmity,’ for the restoration of ‘peace.’ … [I]t is primarily a matter of removing that which stands in the way of the right relationship between God and (in the most comprehensive sense of the word) the world; in other words, of the eschatological restoration of all things.”
Of particular interest for understanding the eschatological aspect of Paul’s conception of life is his statement in 5:10, “For if while we were enemies we were reconciled to God by the death of his Son, much more, now that we are reconciled, shall we be saved by [ἐν] his life.” The reference to the “life” of the Son comes after mention of his “death,” which leads us to understand it not as his earthly life, but specifically as his resurrection life in the power of the Spirit (1:4). John Murray observes,
It is not simply the resurrection as an event that is in view, however. Paul does not say, we shall be saved by his resurrection, but ‘by his life,’ and therefore it is the exalted life of the Redeemer that is intended. The resurrection is in the background as conditioning the exaltation life.
In what sense, then, are we saved by the resurrection life of the Son? To answer that we need to first point out that the salvation envisioned here appears to be eschatological, which is evident from the reference to the wrath of God in v. 9. Therefore, it seems Paul has in mind the firstfruits or firstborn concept, which he develops elsewhere (see Rom. 8:29; 1 Cor. 15:20-24). The preposition ἐν could be translated as “in” instead of “by”—we are saved in his life. The resurrection life of Christ is the guarantee of the resurrection life of all united to him in the same way the full harvest is united to the firstfruits. The life of Christ consisting in his royal eschatological enthronement beyond the reach of the grave in the incorruptibility of the Spirit guarantees the kingdom life of all believers who will share in his reign (5:17) and inheritance (8:17). Murray drives the point home well:
The a fortiori argument of the apostle is thus apparent. It is to the effect that if, when we were in a state of alienation from God, God showed his love to such an extent that he reconciled us to himself and instated us in his favour through the death of his own Son, how much more, when this alienation is removed and we are instated in his favour, shall the exaltation life of Christ insure our being saved to the uttermost. … This argument also shows the indissoluble connection that there is between the death and resurrection of Christ and that since these may never be disassociated so the benefits accruing from the one may never be severed from those accruing from the other. … Hence those who are the beneficiaries of Jesus’ death must also be the beneficiaries of all that is entailed in his resurrection life.
The eschatological life of the believer can never be separated from the resurrection life of Christ. This royal life of the Son in the incorruptible power and glory of the Spirit is the guarantee of the full possession of life for all who believe. Furthermore, as Paul will go on to demonstrate, the only other alternative to life in Christ is death in Adam (5:12-20)—in these two public persons is the whole of humanity subsumed. The path of life from the mode of the flesh, which is subject to death, to the mode of the Spirit, which is characterized by power, glory, and life, is exclusively found in the resurrection life of Jesus Christ our Lord. The gospel, of which the death and resurrection of the Son is the central subject matter (1:3), is the power of the risen Lord to bring all who receive it by faith into this kingdom life.
Lastly, Paul’s connection between reconciliation and life in this passage highlights the God-centered nature of this life, which has been evident since the beginning. There is no life post-fall apart from reconciliation between God and the sinner. This life in Christ can only be considered true life if it is enjoyed in the presence of the living God with all elements of enmity and separation caused by sin blotted out, removed as far as the east is from the west, cast forevermore into the depths of the sea—here legally, as to justification, and later as to sin’s power in sanctification (Rom. 6).
 This is the same sequence as 1:3-4. In other words, the life-experience of Christ is repeated in those united to him by the Spirit through faith.
 This is the first time the title “Son” has been used since the prologue.
 Both justification and sanctification are kingdom benefits with neither being the source of the other, but both being conferred in union with Christ (which is to be transferred into his kingdom) by the Spirit through faith.