A couple of fundamental assertions (propositions):
There is NO GOSPEL apart from Christ Jesus, as per 1 Corinthians 15:1-5
Apart from Christ Jesus there would still be NEWS -- but the NEWS wouldn't be good (for sinners!) The NEWS would be the LORD is the Almighty Sovereign Ruler of Heaven & Earth. His Kingdom is forever!
That NEWS is only good because of Christ Jesus.
Sometime after the birth of the Church at Pentecost, GOD reveals, "to His holy apostles and prophets by the Spirit" a mystery component to the Gospel. And That is what we are discovering, learning about in Ephesians, chapter 3.