Why did Paul write the epistle to the Romans?
Paul seems to have gained knowledge of some ongoing disputes between the Jewish and Gentile Christians, and his seems to have been one of his major concerns as he wrote, although the letter is multi-dimensional. Paul wrote a unified message to the Roman Christians, believing that Christ had called the church to be a unified body. Paul used this motif to bring to these new Christians not only the message of unity, but to impart to them a message of the gospel of grace that comes to all who are in Christ.
It is essential to grasp the overarching theme of Romans in order to gain greater insight into the letter's content and Paul's purpose in writing. Paul wrote to address the tension that had risen between the law and the gospel, Jew and Gentile, God's old-covenant people and His new-covenant people. He was trying to communicate his understanding of these issues according to the gospel. It is a message of unity. God had promised salvation to the world first through Abraham and Israel, but it would ultimately come to realization through a divine mediator in the person and work of Jesus Christ. Salvation had come and in order to further this gospel, this good news of God's grace, it was essential that believers be united through this message of hope and in a common faith in Jesus Christ.