Romans 15:18-19 : For I will not dare to speak of any things save those which Christ wrought through me, for the obedience of the Gentiles, by word and deed, in the power of signs and wonders, in the power of the Holy Spirit; so that from Jerusalem, and round about even unto Illyricum, I have fully preached the gospel of Christ. Many of Paul's Gentile converts were effective workers in the Lord's vineyard, and he might have claimed some credit for their successes; but he did not he would speak only of the things which Christ wrought through him, "for the obedience of the Gentiles." His language does not fit in with, the theory that human agency has no part in the conversion of sinners, but it does fit in with what the Lord said to him in giving him his commission, namely, "to open their eyes, that they may turn from darkness to light and from the power of Satan unto God, that they may receive remission of sins and an inheritance among them that are sanctified by faith in me" (Acts 26:18).
An authority works through its agents or ambassadors. There is nothing mysterious about that. Paul was Christ's agent for the purpose of bringing about obedience among the Gentiles; in that way Christ worked through him, "by word and deed"--by his preaching the gospel, and performing miracles to show that God was with him. The Holy Spirit enabled him to preach and to perform signs and wonders signs to confirm his preaching, and wonders to amaze the people. "From Jerusalem, and round about even unto Illyricum," shows the wide scope of territory Paul covered in his preaching.