Was Paul writing to Jewish or Gentile believers in Romans?

Les teaches that Paul always writes to the believer who is predominantly Gentile. He clarifies that he says predominantly because Jews are certainly eligible for this salvation and many Jews are coming to know the Lord, but it is predominantly God dealing with the Gentile. Therefore, Paul writes to the church at Rome, as well as to believers today, emphasizing that by the deeds of the law no flesh shall be justified, for by the law is the knowledge of sin. Even though the law could not bring someone into salvation, God provides something that does.