What does Romans 15:22 mean?

Paul is nearing the end of his long letter to the Christians in Rome. He has just revealed that his mission from God has been to take the gospel to people who have never heard about Christ. His particular quest is to introduce the gospel to regions where Christ has never been preached. In that way, Paul saw his work as a fulfillment of ancient prophecies.

This prior commitment to his work is the reason Paul refers to in this verse. That is why, he now writes, he has not yet been able to travel to Rome to visit with the Christians there. He kept finding new territories in his part of the world where the gospel had not yet been preached. He had to fulfill his mission to introduce each region to Christ. This hindered or prevented him from traveling to Rome, since a group of believers had already been established there by the work of others.