“God himself is just and at the same time justifies the one who lives on the basis of faith in Jesus [3:26]. Hence, Paul can signify (in a typically Jewish manner) both poles of the event of justification with the one concept ‘the righteousness of God’: the gracious activity of God himself and the end result of the divine work in the form of the righteousness granted to the sinner.
Ever since Adolf Schlatter’s major commentary appeared in 1935, the ‘righteousness of God’ has been gladly seen in German research to be the main theme of the letter to the Romans…Is this delineation of the theme just another example of a typical German propensity for systematizing, or has something correct been seen here?
The answer is entirely dependent upon how much breadth one gives to the expression ‘the righteousness of God,’ so important for Paul (and then for Luther and the reformers). If what is meant by this notion is merely the salvation of the individual sinner–or to put it in Luther’s words, ‘die Gerechtigkeit, die vor Gott gilt’ (i.e., ‘the righteousness which is valid before God’)–then the letter to the Romans actually extends beyond this individual perspective from perhaps as early as 5:12 (the contrast between Adam and Christ), but without a doubt from chapter 9 on. But if what is meant by the expression derived from the Old Testament, ‘the righteousness of God,’ is the entire redemptive activity of God in Christ from creation to redemption, then the theme ‘the righteousness of God’ holds the letter to the Romans together, both from the standpoint of the history to salvation and christologically, while at the same time giving to the gospel of Jesus Christ a world-wide dimension. In my opinion, Rom. 3:21-31 shows convincingly that historically we ought not confine the biblical idea of ‘divine righteousness’ in Paul to ‘the righteousness which is valid before God,’ but that we must allow the word the breadth which is inherent in it from the Old Testament: according to Paul, the one God acts in and through his one Son, Christ, on behalf of the entire world. Christ is his righteousness in person. The work of salvation begun by God in Christ will thus only be completed when the world must no longer sigh under death and transitoriness (Rom. 8:18ff) and when God’s chosen possession, Israel, will have experienced the redemption and fulfillment of the irrevocable promises of God concerning his people in the Parousia of Christ Jesus (cf. Rom. 11:25ff). In this way the arc of tension is drawn tightly from Romans 1 through Romans 11.
But chapters 12-16 are also to be classified under the theme ‘the righteousness of God’ for two reasons. First, and above all, because God in Christ does not just declare those who believe to be righteous on the basis of grace, but at the same time, in doing so, lays hold of them anew in obedience. The new life that the justified obtain is thus called, according to Rom. 6:15ff., a ‘slavery to righteousness’ and finds its God-pleasing expression in the new way of life which the Christians lead. Second, chapter 12-16 belong inextricably to the letter to the Romans because the apostle nowhere (and certainly also not in Romans) expounds abstract theology, but always only concrete exhortation. Whether the Romans really believe in Christ as their redeemer and Lord will be evident, according to Paul, by how they (as Gentile and Jewish Christians) deal with one another and how they resolve the tensions among one another in Rome (cf. ch. 14). Whether the Christians are actually living from and in God’s righteousness is demonstrated in the life of the community within and without. Romans 12-15 are thus the practical test case for the justification which Paul teaches…
Thus, the letter to the Romans has as its theme the Pauline gospel of the divine righteousness in Christ or, for short, the righteousness of God (in and through Christ).” (Peter Stuhlmacher, “The Theme of Romans,” in The Romans Debate, 2nd ed., pp. 340-42)
From The Romans Debate, 2nd ed.