" For I am not ashamed of the gospel of Christ, for it is the power of God to salvation for everyone who believes, for the Jew first and also for the Greek.
For in it the righteousness of God is revealed from faith to faith; as it is written, "The just shall live by faith."- Romans 1:16-17
Paul was not ashamed of the gospel. He had confidence in his message, and he gave several reason that explained why he was not ashamed.
First, The Origin of the gospel: It is the gospel of Christ.
So what is the gospel of Christ? It is Good News, it is Good News that
Christ died for our sins according to Scriptures
He was buried
He rose again and He is alive today.