Romans 1:1,2

Paul, a servant of Jesus Christ Though once a bitter persecutor; called to be an apostle And made an apostle by that calling. The Greek, κλητος αποστολος, is literally, a called apostle, or an apostle called, namely, expressly, as the other apostles were. When God calls he makes what he calls. The name apostle was sometimes given to different orders of men, Romans 16:7, but in its highest sense it was appropriated to the twelve, whom Christ appointed to be with him, Mark 3:14, and whom, after his resurrection, he sent forth to preach the gospel. As the Judaizing teachers disputed his claim to the apostolical office, it is with great propriety that he asserts it in the very entrance of an epistle wherein their principles are entirely overthrown. And various other proper and important thoughts are suggested in this short introduction: particularly the prophecies concerning the gospel; the descent of Jesus from David; the great doctrines of his Godhead and resurrection; the sending the gospel to the Gentiles; the privileges of Christians; and the obedience and holiness to which they were obliged, in virtue of their profession. Separated unto the gospel of God Namely, to preach and propagate it. Separated by God, not only from the generality of other men, from other Jews, from other disciples, but even from other Christian teachers, to be a peculiar instrument of God in spreading the gospel. It is said, Acts 13:2, Separate me Barnabas and Saul, for the work whereunto I have called them. But, this being nothing but a separation of Paul from the teachers at Antioch, to go and preach to the Gentiles, the higher separation, mentioned Galatians 1:15, is here intended. The gospel is here said to be God's, because it is good news from God, than which a greater commendation of it cannot be conceived. Which he had promised afore Of old time, frequently and solemnly: and the promise and accomplishment confirm each other. The promise in the Scriptures, that the gospel should be preached to the Gentiles, is taken notice of by the apostle, to convince the unbelieving Jews that in preaching to the Gentiles he did not contradict, but fulfil the ancient revelations.