Carson, D.A., and Douglas Moo An Introduction to the New Testament - Second Edition. Grand Rapids: Zondervan, 2005. "New Testament Letters" Carson & Moo pp. 331-353
"Romans" Carson & Moo pp. 391-414
p. 391 "Romans is the longest and most theologically significant of the letters of Paul, 'the very purest gospel' (Luther). The letter takes the form of a theological treatise framed by an epistolary opening and closing. The opening contains the usual prescript and thanksgiving and is concluded with a transitional statement of the theme of the letter: the gospel as the revelation of God's righteousness, a righteousness that can be experienced only by faith."
On pp. 391-392 Carson and Moo outline the body of the book in four parts: "The gospel as the righteousness of God by faith (1:18-4:25). . . The gospel as the power of God for salvation (5:1-8:39) . . . The gospel and Israel (9:1-11:36) . . . The gospel and the transformation of life (12:1-15:13)."
Romans claims Pauline authorship, a claim which is not seriously disputed. Dating is a bit more complicated. Paul discusses the fact that he is going to Jerusalem and that he wishes to go to Rome on his way to Spain. Carson and Moo consider that the most likely place of authorship was Corinth, from where Paul may well have gone toward Jerusalem about 57.
The situation of the church at Rome is also possibly problematic. Carson and Moo do not think that Peter is likely to have founded a church in Rome prior to the time Paul would have written Romans. They also do not think it likely that Paul would make a visit such as he describes in Romans 1:8-15 to a church founded by another apostle. Rather, they suggest that the church in Rome was founded by Jews who had been present in Jerusalem at Pentecost.
Carson and Moo discuss the text of Romans on pp. 398-401. There are some suggestions of interpolations and redactions, mostly spurred on by the doxology found in 16:25-27, which "is omitted in some manuscripts and appears at different places in others" (p. 399). Carson and Moo consider that the text has always had all sixteen chapters and that it is simply slightly uncharacteristic of Paul's letters, but not necessarily inauthentic.
As to the genre of Romans, it is more like a treatise of doctrine than a personal or typical epistolary letter. The purpose is clearly to lay out doctrines in detail. Numerous possible purposes for composition have been put forward. There are few statements about the purpose of the letter, though it is clear that Paul is intending to introduce his plan to visit. We may find it more fruitful to look at multiple reasons for writing, based on the different types of information contained in the letter.
The theme of Romans has likewise shifted in scholarly opinion. Interestingly enough, Carson and Moo trace the locus of the theme moving from near the beginning, with the Reformational focus on justification by faith, to the union of Christ and the Church in chapters 6-8, to salvation history in 9-11, and to exhortations to unity in 14-15. Currently all four positions are alive.
In summary, the book seems to have undergone lively and varied scholarly discussion. It is a lively and varied book which lends itself well to such research and commentary.