John Calvin Commentary Romans 15:17

"I have therefore my glorifying in Christ Jesus in things pertaining to God." — Romans 15:17 (ASV)

I have then, etc. After having generally commended his own calling, so that the Romans might know he was a true and undoubted apostle of Christ, he now adds testimonies by which he proved that he had not only undertaken the apostolic office conferred on him by God’s appointment, but had also eminently adorned it.

At the same time, he records the faithfulness he had shown in carrying out his office. Indeed, it is of little use to be appointed, unless we act according to our calling and fulfill our office.

He did not make this declaration from a desire to attain glory, but because nothing was to be omitted that might gain favor and authority for his doctrine among the Romans. It was in God, then, not in himself, that he gloried, for he had no other aim than that all the praise should return to God.

That he speaks only negatively is indeed an evidence of his modesty, but it also served to lend credibility to what he was about to announce, as though he were saying, “Truth itself gives me such cause for glorying that I have no need to seek false praises, or those belonging to another; I am content with praises that are true.” It may also be that he intended to counter the unfavorable reports which he knew were everywhere spread by malicious people. He therefore mentioned beforehand that he would speak only of things well known.