Romans 1:2

2.Which he had before promised, etc. — As the suspicion of being new subtracts much from the authority of a doctrine, he confirms the faith of the gospel by antiquity; as though he said, “Christ came not on the earth unexpectedly, nor did he introduce a doctrine of a new kind and not heard of before, inasmuch as he, and his gospel too, had been promised and expected from the beginning of the world.” But as antiquity is often fabulous, he brings witnesses, and those approved, even the Prophets of God, that he might remove every suspicion. He in the third place adds, that their testimonies were duly recorded, that is, in the Holy Scriptures.

We may learn from this passage what the gospel is: he teaches us, not that it was promulgated by the Prophets but only promised. If then the Prophets promised the gospel, it follows, that it was revealed, when our Lord was at length manifested in the flesh. They are then mistaken who confound the promises with the gospel, since the gospel is properly the appointed preaching of Christ as manifested, in whom the promises themselves are exhibited. (18)