Paul, a servant of Christ Jesus, called to be an apostle and set apart for the gospel of God—
Paul calls himself a bondslave of Christ Jesus. The case classification is genitive of possession. The apostle is proud of the fact that he is a slave belonging to his Lord. There were certain individuals in the Roman empire designated “Slaves of the Emperor.” This was a position of honor. One finds a reflection of this in Paul’s act of designating himself as a slave of the King of kings. He puts this ahead of his apostleship.
The noun was used of an envoy, namely, one sent on a commission to represent another person, the person sent being given credentials and the responsibility of carrying out the orders of the one sending him. Our word “ambassador” adequately translates it.
Paul, therefore designates himself as a divinely and effectually summoned ambassador of the Lord Jesus, sent by Him on a commission with credentials, the commission, to evangelize the Gentile world, his credentials, miracles.