Romans 15:23-24 meaning

Paul found that there were no more areas in this region that lacked the gospel. He writes that with no further place for me in these regions (v 23), he now has the opportunity to visit Rome. He has wanted to do this for a long time, but only now has the opportunity due to having exhausted places that needed to hear the gospel for the first time. 

Paul says Since I have had for many years a longing to come to you (v 23), he begins to make plans to go see the believers in Rome by way of his visit to Spain, which at this point was under Roman control. Whenever I go to Spain—for I hope to see you in passing, and to be helped on my way there by you, when I have first enjoyed your company for a while (v 24).

What we now know as Italy would have been on the way to Spain, so Paul is planning to drop by to see the Roman believers on his journey. 

Paul thinks very highly of the believers in Rome and knows he will enjoy and be encouraged by their company. In Chapter 1, he more fully explained what he hoped to gain from his visit with the believers in Rome:

"For I long to see you so that I may impart some spiritual gift to you, that you may be established; that is, that I may be encouraged together with you while among you, each of us by the other's faith, both yours and mine."
(Romans 1:11-12) 

Paul hoped to encourage the believers there and help them grow. He knew that the time together would encourage him as well. Throughout this letter to the Romans, Paul has emphasized the importance of believers caring for one another. In Romans 12, Paul talked about the church as a body, with each member doing its part to help the others, and to work together to serve the Head, which is Christ. Paul planned to visit and encourage the believers in person and knew they would do the same for him and help him with his physical needs as well.