A good article on why Paul wrote the book of Romans from a solid scholar. This is not an easy read, but well worth the trouble.
"To the question “What is Romans all about?” a variety of answers might be given, and, in
fact, have been given. Most students see the Epistle as concerned basically with the salvation
of man. Sometimes this is understood in general terms,1 sometimes in terms of the gospel,2 or
perhaps with specific reference to justification." Read More.