Paul's gives us the outline for the Letter to the Romans right up front:

For I am not ashamed of the gospel because it is the power of God that brings salvation to everyone who believes: First to the Jew, then to the Gentile. For in the gospel, the righteousness of God is revealed--a righteousness that is by faith from first to last, just as it is written: "The righteous will live by faith."

Pretty much everything in the rest of the letter is acknowledged here in these two short verses.