The main message of the Bible about Jesus Christ can easily become mixed with all sorts of things that are related to it. We see this in the way people define or preach the gospel. But it is important to keep the gospel itself clearly distinct from our response to it or from the result of it in our lives and in the world. If our proper response to the gospel message is faith, then we should not make faith part of the gospel itself. It would be absurd to call people to have faith in faith! While the new birth bears a close relationship to faith in Christ, it is a mistake to speak of the new birth as if it were itself the gospel. Faith in the new birth as such will not save us.
It is, therefore, important to understand both what the gospel is, so that we include what must be believed, and what the gospel is not, so that we don't require people to believe more than is necessary for salvation.
-- p. 81, According to Plan by Greame Goldsworthy
Now, if you are curious about what Graeme Goldsworthy, the author, will say about the gospel, and see whether he really got it right or not, I invite you to actually read this important book.
You can get it from Koorong or Amazon.