Why does Paul write the Epistle to the Romans? Unlike many other NT epistles, it is not very clear that there is a specific false teaching, or false teacher or group of false teachers that Paul is gunning for. It is possible that he is contributing his penny's worth to a debate among the Roman Christians (in which case, likely a debate between Jewish Christians and Gentilic Christians). But I wonder if Paul, excited by the prospect of visiting the great city, is taking the opportunity to offer his maturing (if not mature) thinking on the gospel. After all, as an intellectual Jew called to preach to Gentiles, as a scholar of the Hebrew scriptures reckoning with the spreading flame of the gospel beyond Israel, Paul at some point had to confront with honesty and rigour the questions Romans addresses: what is God's vast eternal plan? How do the Jews figure in this plan? Who may be saved and how might they be saved? What now is the point and purpose of the Law? How are Christians to live in a post-Law, Gentile-including dispensation?
But the gospel is the gospel of Jesus Christ so we also find in Romans a concerted effort to explain the role and significance of the man Jesus of Nazareth 'descended from David according to the flesh and was declared to be the Son of God in power according to the spirit of holiness by his resurrection from the dead, Jesus Christ our Lord' (1:3-4).