It is generally agreed that Rom 1:16f encapsulates the theme of Romans.  Bob Yarbrough writes that ‘the powerful “good news” of which Paul is not ashamed sheds definitive light on any number of issues that world fallenness and the human dilemma pose:-

• Do you seek personal salvation? Many thank God for the direction of Romans 10:9–10.
• Does a believer seek a road map for daily living? It’s hard to beat Romans 12:1–2.
• Is the need for grasping the human condition and God’s assessment of it? See Romans 1:18–3:20.
• Is the question how God justifies the ungodly? Romans 3:24–26 covers the mechanics of the atonement, augmented by the equally significant resurrection (Rom. 1:4; 4:25).
• Do we need help with ecclesial identity? Since Christians are children of Abraham through faith, Romans 4 is more important than is often realized.
• Is the need to make sense of the world’s paroxysms and pathologies, including Christian suffering? See Romans 8.
• Are there questions about the abiding importance of Israel, about how the gospel can be true if most of the descendants of Abraham in Paul’s time are rejecting it, or how God can be regarded as faithful to his old covenant promises when the Gentiles have eclipsed the Jews in their embrace of the gospel? See Romans 9–11.