Why did Paul have to declare to the Roman Christians "I am not ashamed of the Gospel of Christ"?
The power of God, reckoned to us in the Gospel, accords righteousness to us, something we do not and cannot earn, all because of what Jesus did at the Cross.
Paul was emphatic and unshakable in his declarations:
"Be it known unto you therefore, men and brethren, that through this man is preached unto you the forgiveness of sins: 39And by him all that believe are justified from all things, from which ye could not be justified by the law of Moses." (Acts 13: 38)
This revelation of the New Covenant, in which Jesus fulfilled the Old and ushered away the Law of Moses for the Faith of Christ, created immediate joy --- and division:
"And when the Jews were gone out of the synagogue, the Gentiles besought that these words might be preached to them the next sabbath. 43Now when the congregation was broken up, many of the Jews and religious proselytes followed Paul and Barnabas: who, speaking to them, persuaded them to continue in the grace of God." (Acts 13: 42-43)
Stephen, the first martyr of the Body of Christ, was roundly condemned and ultimately executed for preaching the Gospel:
"When they heard these things, they were cut to the heart, and they gnashed on him with their teeth. 55But he, being full of the Holy Ghost, looked up stedfastly into heaven, and saw the glory of God, and Jesus standing on the right hand of God, 56And said, Behold, I see the heavens opened, and the Son of man standing on the right hand of God. 57Then they cried out with a loud voice, and stopped their ears, and ran upon him with one accord, 58And cast him out of the city, and stoned him: and the witnesses laid down their clothes at a young man's feet, whose name was Saul. " (Acts 7: 54-58)
Paul was arrested and nearly killed by fellow Jews for preaching the Grace of God:
"And when the seven days were almost ended, the Jews which were of Asia, when they saw him in the temple, stirred up all the people, and laid hands on him, 28Crying out, Men of Israel, help: This is the man, that teacheth all men every where against the people, and the law, and this place: and further brought Greeks also into the temple, and hath polluted this holy place."" (Acts 21: 27-28)
Yet Paul writes to the Romans: "I am not ashamed of the Gospel"
Shame is the greatest force which Satan has used to stifle the preaching of God's Word.
The number one reason why people avoid preaching the full Gospel? The contention that it gives license for people to keep on sinning:
"What shall we say then? Shall we continue in sin, that grace may abound? 2God forbid. How shall we, that are dead to sin, live any longer therein? (Romans 6: 1-2)
Here is how Paul responds to such hateful deception:
"3Know ye not, that so many of us as were baptized into Jesus Christ were baptized into his death?4Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life." (Romans 6: 3-4)
We are not ashamed of the Gospel, because through Jesus' Work we are taken from dead in our trespasses to alive and seated in heavenly places in Him (Ephesians 2: 4-6)
We are made the righteousness of God in Christ (2 Corinthians 5: 21), and thus we rest assured in Him that "no weapon formed" against us can prosper (Isaiah 54:17)
We are not ashamed of the Gospel, because through God's grace, we are restored and redeemed, redefined by His righteousness.