What does Romans 15:29 mean?

Paul makes a declaration about his plans to visit the Christians in Rome. He is convinced that when he finally gets to them, he will arrive in the fullness of Christ's blessing. In other words, Paul knows that he will come with Christ's blessing or approval and that his presence with the Roman Christians will be Christ's blessing to them, as well.

Paul is confident that his comings and goings are dependent on Christ's blessing. He also recognizes how such travels serve the purpose of Christ blessing others through him. All believers can live with this confidence, as well, if we are willing to be used by God in this way.

However, that confidence does not mean we can ever claim perfect knowledge. We don't know the circumstances under which God will use us to bless others. Paul, for instance, did not likely anticipate the path that would finally bring him to Rome. Acts chapters 27–28 contain that surprising and powerful story. Because of the events described there, it is unknown if Paul ever reached Spain.