Epistle to the Romans
Paul wrote the letter to the Romans to explain a very important point in Christianity. He proves, by quoting the Old Testament, that all humankind is guilty of sin before God. People whom God calls righteous can only do so by trusting in God's ways, and not by their own effort.
Once this belief is had, the believer receives the Holy Spirit, who helps the believer live a new life. Paul asks the Romans to observe Christian ethics and submit themselves to authorities.
The letter remains very influential in explaining to non-Christians and new Christians what their Christian belief is all about.