The Book of Romans is Pauls theological masterpiece. Paul lays out the crucial doctrine of Justification (that God declares the unrighteous to be completely righteous because of the work of Jesus Christ). It is upon this pillar that he builds his argument for the gospels power to transform unrighteous sinners into the justified righteous, for the cross of Jesus Christ can make us righteous. The good news in Christ is we can become justified, just as if we never sinned!
Scripture References: Romans 1:16-17