What does Romans 15:20 mean?
There's nothing wrong with preaching the gospel of Christ in an area where it has already been preached. In fact, that preaching must continue. It's not feasible to put that message in front of every living person in a region all at once. People are born and move into and out of those areas all the time. Others need to hear the message more than once to fully understand it. Paul, though, grasped that staying to re-preach the good news was not his mission. God had given him a more specific work to do.Ambition is a good thing when it is bent toward a good purpose. Paul's ambition was to preach the gospel only to what we call today "unreached peoples." His work was not to build on the work done by other preachers before him. His work was to break new ground, to bring the truth of God's grace to new ears.
This fits with what he wrote in the previous verse that he has fulfilled his ministry in a large number of places, introducing the gospel for the first time in many cities and regions. What an honor Paul was given: to introduce to so many people the news of the amazing opportunity to be made right with God through faith in Christ.