Romans was intended to convey the message of the righteousness
of God and how it is revealed and vindicated, and how mankind can
access it through faith in Christ. It is a presentation of the plan
The Apostle Paul wrote it because the apostles were dying out and there had been heresy in the early Church. The Apostle Paul actually was a Roman citizen and he wanted his fellow citizens to believe in the Lord Jesus Christ. Hope this helps you! God bless!