16For I am not ashamed of the gospel, for it is the power of God for salvation to everyone who believes, to the Jew first and also to the Greek.Paul is not ashamed of the preaching of the Gospel because in the Gospel is revealed the righteousness of God, God's faithfulness. It is in the Gospel that the promise to rescue Israel from exile and bondage is being revealed in sending the Messiah to rescue Israel (and the nations too) and to establish the city promised to Abraham. In the Gospel is being revealed the faithfulness of God.
On the contrary, this opening thematic statement is not saying, "I am not ashamed of the Gospel for in it is revealed a means for sinful humanity to receive a righteousness from God in order to be reconciled to Him". Of course this too is revealed in the Gospel but that is not what the over arching Glory of the book of Romans is about. Romans and the driving force and foundation of our faith is the knowledge of God. The gospel is about God and His faithfulness and this faithfulness to rescue a broken humanity and set the world right and establish the kingdom, this faithfulness of God is being revealed in the Gospel. God has fulfilled the promises to Israel to deliver her from her enemies. He has sent Messiah to rule all the world and those who believe who have faith in His faithfulness these are the people who live and persevere and live in shalom in this life.