Matthew Henry on Romans 15:14-21

The apostle was persuaded that the Roman Christians were filled with a kind and affectionate spirit, as well as with knowledge. He had written to remind them of their duties and their dangers, because God had appointed him the minister of Christ to the Gentiles. Paul preached to them; but what made them sacrifices to God, was, their sanctification; not his work, but the work of the Holy Ghost: unholy things can never be pleasing to the holy God. The conversion of souls pertains unto God; therefore it is the matter of Paul's glorying, not the things of the flesh. But though a great preacher, he could not make one soul obedient, further than the Spirit of God accompanied his labours. He principally sought the good of those that sat in darkness. Whatever good we do, it is Christ who does it by us.