Sometime ago, John Piper preached a sermon, “Did Jesus preach Paul’s Gospel?” In contrast, Scot McKnight has a sermon called “Did Jesus preach the Gospel?”
I tried to embed it but couldn’t, but do watch it, it only goes for 18 minutes!
As to how Jesus’ messiahship in the Gospels figures in the “gospel,” see my forthcoming Jesus is the Christ: The Messianic Testimony of the Gospel.