What does Romans 15:18 mean?
Here Paul models for us how believers can be proud of our work while still walking in humility. In short, Paul refuses to take personal credit for his accomplishments. Christ has accomplished this work through him. Though Paul is the one who obeyed, he merely participated in the work Christ was accomplishing. He recognizes himself as an instrument of God to be used for God's purposes.Still, he is proud of what God has used him to accomplish—bringing the Gentiles to obedience. Paul emphasizes the obedience of the Gentiles here and not their faith. He has been clear throughout Romans that belief in Christ itself is an act of obedience to God (Romans 1:18–23). In addition, faith in Christ leads to greater obedience to God in all areas of life as we walk in the Spirit.
Before Christ, nobody would have expected the larger Gentile world to begin to live in obedience to Israel's God. Paul is fulfilling his mission to take the gospel to the Gentiles and, by Christ's power through him, many Gentiles around the world have begun to come to God, to obey by believing in Christ. Paul recognizes that he is at the forefront of a world-changing movement.
He begins to list how Christ has accomplished this work through him, beginning with "word and deed." Paul has used words to spread the good news of salvation through faith in Christ far and wide. His deeds have included heroic acts of service, as well as miraculous signs and wonders.