Paul, a servant of Christ Jesus, called to be an apostle and set apart for the gospel of God—the gospel he promised beforehand through his prophets in the Holy Scriptures regarding his Son, who as to his earthly life was a descendant of David, and who through the Spirit of holiness was appointed the Son of God in power[ by his resurrection from the dead: Jesus Christ our Lord. Through him and for his name’s sake, we received grace and apostleship to call people from among all the Gentiles to the obedience that comes from faith
2.The gospel is not new
“The gospel he promised beforehand through his prophets in the Holy Scriptures” (verse 2).
Paul is at pains to show that the gospel he preaches, God’s gospel, is not new. Indeed the gospel was promised by God beforehand through the Old Testament prophets. That which is now preached is that which God always had in mind. The way God brings people to himself has not changed (Isaiah 45; Galatians 3:8).
The gospel today is in conformity with God’s continuing revelation and is the final expression of it. Jesus of Nazareth was recognised as the perfect fulfilment of all that God had foretold through the prophets about his Messiah. The aged Simeon, quoting from Isaiah 42:6, described the child Jesus as “a light for revelation to the Gentiles and for the glory of your people Israel” (Luke2:29-32)
Peter in his sermon at the temple in Jerusalem after the healing of the crippled man at the beautiful gate (Acts3:32), asserts that Jesus is the Prophet whom Moses foretold in in Deuteronomy 18:15,16.
In his sermon on the day of Pentecost (Acts2:14-36), Peter claims Jesus is the fulfilment of God’s promise in Psalm 132:11 (Acts 2:30) and that it was really Jesus of whom David had spoken in Psalm 16:8-11 (Acts 2:25-28)