Romans 16:25-27 (NIV)
Now to him who is able to establish you by my gospel and the proclamation of Jesus Christ, according to the revelation of the mystery hidden for long ages past, but now revealed and made known through the prophetic writings by the command of the eternal God, so that all nations might believe and obey him-- 27 to the only wise God be glory forever through Jesus Christ! Amen.
Paul's benediction closes his letter to the Romans, perhaps the greatest treatise on how a sinful man can be made righteous before a holy God.
Paul mentions that what he has been preaching is according to revelation of a mystery given by the commandment of God. So what is this mystery which had been hidden since the world began but is now made known? There are many mysteries mentioned in the New Testament but the most common is that salvation is available to everyone, both Jew and Gentile. The redemption we have in Jesus Christ is the central theme of the Bible. It is found concealed in the Old Testament and revealed in the New Testament. Take a look at what Jesus himself had to say about this mystery.
Luke 24:44-47 (NIV)
He said to them, "This is what I told you while I was still with you: Everything must be fulfilled that is written about me in the Law of Moses, the Prophets and the Psalms."
Then he opened their minds so they could understand the Scriptures. He told them, "This is what is written: The Christ will suffer and rise from the dead on the third day, and repentance and forgiveness of sins will be preached in his name to all nations, beginning at Jerusalem.
Only an infinitely wise mind could have conceived such a marvelous plan of redemption. God, the holy Creator and Judge of the universe would become a man, acquainted with the same grief we are subject to. He would become our go-between, our mediator and advocate. He would take our sins away, paying the penalty in our behalf. How else could God be both holy and merciful? To God be the glory!