Romans 15

And so I have made it my aim to preach the gospel, not where Christ was named, lest I should build on another man’s foundation. v.20

Read chapter 15
Paul had never visited these in Rome before he wrote this letter to the Romans!  The Jews in Rome who Paul is writing to had heard the gospel yet through another apostle.  Paul was writing them to clear up matters of being Jewish believers in Jesus Christ and did finally visit them as we see in Acts 28 at the end of his ministry.  Paul says that his desire was not just to backup someone but present new the gospel of Christ as to why he hadn't come to them yet.   We read at the beginning of this letter Paul saying, "Now I do not want you to be unaware, brethren, that I often planned to come to you (but was hindered until now), that I might have some fruit among you also, just as among the other Gentiles. I am a debtor both to Greeks and to barbarians, both to wise and to unwise. So, as much as is in me, I am ready to preach the gospel to you who are in Rome also" (Romans 1:13-15).
Paul's desire was to proclaim the message of Christ to where it had not been heard yet. 
Often it's a lot easier to be a support to a Christian leader who's already built a foundation with a community than to be the one starting from scratch.  
Christ may have been proclaimed in your community, but how can you still pave a way of those that are "forgotten" or "unreached" to develop them their walk with Christ or present the gospel to them in a way they haven't fully comprehended?  I always say I thought I was a Christian till I became a Christian. Often one may accept and believe in Jesus Christ but stop there.  How edifying it is to have godly influences to help direct us to live a life for Christ.  Who can you be that to?  Who has been that for you?