John Nelson Darby expounds on Romans chapters 2 to 4, emphasizing the universal guilt of both Jews and Gentiles before God due to sin, and the futility of seeking righteousness through the law. He highlights that true righteousness comes through faith, as exemplified by Abraham and David, and is made possible by the redemptive work of Christ. Darby stresses that God's righteousness is revealed apart from the law and is accessible to all who believe, providing a foundation for justification and peace with God. He concludes that believers are justified freely by grace through faith in Christ, who has borne the penalty for sin and offers a new life in Him.