As the truth of Christ is in me.. — The formula is almost, though not quite, of the nature of an oath. He speaks here, as in Romans 9:1, in the consciousness that the truth of Christ (the objective sense of the truth revealed in Christ seems almost merged in the subjective sense of the truthfulness that was of the essence of His nature) dwells in him, and that therefore he cannot but speak “the truth, the whole truth, and nothing but the truth.”
No man shall stop me of this boasting. — Literally, This boast shall not be stopped for me. The verb for “stop” means primarily to “hedge round,” or “fence.” In the New Testament, as in Romans 3:19, it is always used of “stopping the mouth.” Here, with something like a personification, he says that his boast shall not have its mouth thus sealed.
In the region of Achaia. — The word (klima) is peculiar to St. Paul among the writers of the New Testament (Romans 15:23; Galatians 1:21). Like our word “climate,” which is derived from it, it was originally a term of science, and had passed gradually into colloquial usage. He names the province and not the city — probably to include Cenchreæ. There is no evidence of his having preached in any other locality south of the Isthmus of Corinth.