Romans 1:2

Promised afore. This promise was made specifically in the OT passages that predicted the coming of the Messiah, but was also implicit in the meaning of the entire OT. The gospel was no afterthought on God’s part, neither was it any abrupt change in His steadily unfolding purpose for man. It was but the fulfillment of His promise made to our first parents (see on Gen. 3:15) and to each succeeding generation.

By his prophets. Not only the writers of the prophetic books of the OT but others, such as Moses (Deut. 18:18), Samuel (Acts 3:24), and the psalmist (Ps. 40:7), prophesied of the gospel (cf. Heb. 1:1).

Holy scriptures. Throughout this epistle, Paul frequently refers to passages from the OT to show that the gospel was in full accord with the teachings of the already acknowledged oracles of God (see Acts 26:22, 23). Paul was especially anxious to prove to his own countrymen that Christianity was built on the foundation of their own prophets and holy writings.