Why Did Paul Write Romans?

As a solution to this problem, Frank Matera has proposed that the purpose of Romans is a matter of “both/and” rather than “either/or”. He suggests that Paul writes to: (1) summarize his gospel, (2) prepare his defense at Jerusalem, (3) gain support for the Spanish mission, and (4) resolve the problem of the weak and the strong (Romans,8). I think this view has much to commend it. Letters, speeches, and arguments often come with multiple purposes and can function in a variety of ways. Why should we think the complex argument of Romans should be limited to a single purpose? The apostle Paul was certainly capable of complex thought and nuanced argument intended to accomplish various persuasive goals. Matera’s proposal accounts for the content of Romans and the circumstances both of Paul and the Christians in Rome, and I take it to be quite helpful. We shall have to wait and see how how his argument fares in larger and famed Romans debate.
What do you think? Is Matera’s proposal helpful? What are its strengths? Weaknesses?