The gospel message should not have been new to the Jews in Rome or anywhere.  It was found throughout the Old Testament Scriptures.  Indeed, salvation through Jesus Christ is the real story and purpose behind all of Israel's history.  

Abraham saw Christ by faith (John 8:56), and ancient Job anticipated the Redeemer who would and will stand on the earth (Job 19:25-27).  The prophets were hungry to see the reality of their prophecies (1 Peter 1:10-12).  Simeon and Anna recognised the "hope of Israel" as they held the baby Jesus (Luke 2:25-38).  Augustine is quoted as saying ‘Christ is in the Old (Testament) concealed; Christ is in the New revealed’.  God spoke but Israel chose not to listen.

Religious people, who respect the Old Testament, should be reminded that it points to Jesus.  The Jewish people in Rome had therefore already heard the essence of the gospel message, but not understood it and were not seeking the Lord.  Nevertheless, God revealed Himself to those who were not seeking Him and offered the hope of salvation to people who refused to obey Him – rebellious and backslidden Israel and, later, Gentiles too (Isaiah 65:1).  

It is the same today. God does not only speak to the faithful.  His gospel is for everybody (John 3:16).  He does not only speak to Christians but to people of every religious and ethnic background.  That is why we should not be afraid or ashamed to tell the gospel even if they don't listen, understand, or seek the Lord; and even if they refuse to submit to Him - because that was how God treated Israel.  So we must never write off people who are uninterested or unresponsive to the gospel; it is still the power of God that brings salvation to everybody who believes (Romans 1:16).  The fact that they have not yet believed is not a good reason to exclude them from hearing the gospel!  It is only through the gospel that they will know who and what to believe. If God did not give up on Israel for 1,500 years, why should we give up on our friends?