What is the meaning of Romans 1:5-6?

5 By whom we have received grace and apostleship, for obedience to the faith among all nations, for his name: 6 Among whom are ye also the called of Jesus Christ: (Romans 1:5-6 KJV)

William Burkitt’s Commentary

Observe here, 1. St. Paul declares the person from whom he received authority to be an apostle, namely, Christ himself:  By whom he received apostleship; that is, by Jesus Christ, mentioned in the foregoing verse; who called him immediately, and furnished him with authority and ability for a gospel-preacher, even then when he had been a furious and fiery persecutor.

Observe, 2. He declares how free and undeserved a favour this was; he acknowledges that he had received grace to be an apostle or a messenger of the gospel of Jesus Christ which is a special act and instance of divine grace and favour;  By whom we have apostleship.

Observe, 3. What is the special duty of an apostle, and the great end and design of that honourable function, namely, to call all persons to believe and obey the gospel.

Learn thence, that the great end of the ministry of the word is to bring sinners to believe and obey the gospel of Christ, to persuade them to yield, not a professional subjection only, but real obedience also to the gospel of Christ;  By whom we have received grace and apostleship for obedience to the faith among all nations.

Observe, 4. How the apostle puts the Romans in mind of their condition by nature, before the gospel was revealed to them and received by them; they were then Pagans and heathenish idolators, but now Christians or the called of Jesus Christ, among whom (that is, among the Gentile nations)  ye are also the called of Jesus Christ.

Learn thence, That it is a necessary duty for ministers, and a profitable duty for the people, to put, and be often put in mind of what they were and are by nature; it is profitable, both to increase their humility and also to excite their gratulation. “You Romans (as if the apostle had said)who are now the called of Jesus Christ, were once afar off, even amongst the vile and cursed Gentiles: let the remembrance of what you once were, keep you continually humble, and the knowledge of what now by grace you are, render you forever thankful.”