(15) So, as much as is in me, I am ready to preach the gospel to you who are in Rome also.
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Paul's statement is very significant in terms of what "preaching the gospel" means. Paul, writing to an already established Christian congregation, wanted to go to Rome to preach the gospel to them! Why would he do that? Were they not already converted? Yes, they were! Paul compliments them earlier: "First, I thank my God through Jesus Christ for you all, that your faith is spoken of throughout the whole world" (Romans 1:8). The congregation in Rome was remarkable, renowned for its faith. Can a congregation be recognized for world-renowned faith only upon conversion?
Though Paul had never been to Rome, these Roman Christians had been converted some time earlier after hearing the gospel through other ministers. They were growing, and Paul wanted to add to their growth by giving them more of the gospel, as he says in verses 11 and 12. "For I long to see you, that I may impart to you some spiritual gift, so that you may be established—that is, that I may be encouraged together with you by the mutual faith both of you and me." Then, he adds his desire to preach the gospel to them.
Paul wanted to preach the gospel—more of it, in greater detail—to a congregation of converted people! He wanted to be an instrument to reveal more of its glories to them so they might continue to grow. Clearly, the preaching of the gospel by the ministry continues in the church after conversion.
— John W. Ritenbaugh