This mainly Gentile audience (cf. Romans 1:5-6), familiar with the Old Testament narrative world, needed to be established in the truth, understand the gospel and history, and be assured that the salvation of the Gentiles in the gospel was always God’s plan from the beginning.

All redemptive history culminates in the object of faith, the Son of God, Jesus Christ our Lord:

"...the gospel of God, 2which He promised beforehand through His prophets in the holy Scriptures, 3concerning His Son, who was born of a descendant [Lit seed] of David according to the flesh, 4who was declared the Son of God with power by the resurrection from the dead, according to the Spirit of holiness, Jesus Christ our Lord," (Romans 1:1-4)

It is as if Paul has been laying out all the titles and credentials of this One who has accomplished the gospel and now, finally, presents His name—Jesus Christ our Lord.

Jesus—historical individual, the Man, Jesus of Nazareth
Christ—the Anointed One, the Messiah, the One on whom all Old Testament promises depend
Lord—the primary title of Jesus’ supremacy and right to rule, contrasted to Caesar, often used as a translation of the divine name “Yahweh,” especially when quoting the Old Testament (cf. Romans 10:9-13)

If this One, described in the Old Testament, has arrived and accomplished this work to bring about the gospel, then what will be the result?

Mass Gentile salvation

“...to bring about the obedience of faith among all the Gentiles for His name’s sake,…” (Romans 1:5)

https://youtu.be/e0bLrIDXo7c