The gospel is not brand new, it's "Repent, for the kingdom of heaven is at hand!"

Rom 1:1
Paul, a bond-servant of Christ Jesus, called as an apostle, set apart for the gospel of God,

What does Paul mean here by being "set apart to the Gospel of Elohim?" He means that he has passed beyond the things of the world and is totally dedicated to the message of Yeshua Messiah.

Paul is not longer living for the Talmudic teachings that he learned most of his life. He is now dedicated to spreading the message of Messiah, teaching the ways of Elohim (His Torah), and separated from the traditions of man.

Rom 1:2
which He promised beforehand through His prophets in the holy Scriptures,

The gospel is not brand new. It has been promised by His prophets all throughout the Tanakh. "Repent, for the kingdom of heaven is at hand!" Mark 1:14-15).

Paul discusses the coming of the Kingdom through Yeshua Messiah in the next five verses.

Rom 1:3
concerning His Son, who was born of a descendant of David according to the flesh,

The word "concerning" is the Greek preposition "peri", which is also used in our words pericospe and perimeter. It means "that which encircles." The Gospel circles around the King of the Kingdom, Yeshua Messiah.

His entire title is spelled out here. He is the Son of Elohim. He is our Master. And the statement "He was born of a descendant of David," points out the fact that He was the One who was promised through the seed of David who will rule the Kingdom forever (2 Sam. 12:12-16, Isaiah 9:6-7, Jer. 23:5-6 33:15-17). There is no mistaking the meaning of Him being a "descendant of David." That means He is Messiah to those who know the Tanakh. Rom 1:4 who was declared the Son of God with power by the resurrection from the dead, according to the Spirit of holiness, Jesus Christ our Lord,

The "Spirit of holiness" is the Spirit of Elohim. He was "declared the Son of Elohim with power by the resurrection from the dead." He always was the Son of Elohim, but we saw Him as the Son of Elohim through His resurrection. Yeshua was accurate when He said He was not of this world John 8:23).
Rom 1:5
through whom we have received grace and apostleship to bring about the obedience of faith among all the Gentiles, for His name's sake,

What is grace? Grace is Elohim's method of salvation. Elohim is gracious enough to offer us a salvation we do not deserve. "Obedience of faithfulness" is the key. Faithfulness should bring what kind of obedience? Faithfulness in Yeshua Messiah will bring about obedience of Torah among the Gentiles. Faithfulness in Yeshua will bring transformation of our lives to desire to live according to the Instructions (Torah) of Elohim (Romans 15:18-19, 16:26, Acts 6:7, 2 Cor. 10:4-6, Heb. 5:9).