These chapters deal with the heart of the gospel.
The apostle has announced the theme of Romans: God’s saving power towards us in Jesus Christ for all who believe. In 1.18-3.20, Paul has explained why the gospel is so necessary, why we need a divinely provided righteousness in the incarnate Lord Jesus Christ — because all righteousness is lacking in ourselves, whether we be Gentiles or Jews.
Paul turns to the great question: how can sinful man be justified before God and how can a righteous God be a righteous God and a Saviour?
He speaks in this section about three things: the divine way of justification, the immediate implications of justification and the spiritual blessings of justification.