The Gospel, The Power of God.
Romans 1:14-17 (CSB)
14 I am obligated both to Greeks and barbarians, both to the wise and the foolish. 15 So I am eager to preach the gospel to you also who are in Rome.
The Righteous Will Live by Faith
16 For I am not ashamed of the gospel, because it is the power of God for salvation to everyone who believes, first to the Jew, and also to the Greek. 17 For in it the righteousness of God is revealed from faith to faith, just as it is written: The righteous will live by faith.