The writers of the New Testament are at pains to point out that the Gospel that must be preached is the identical Gospel as preached by Christ and the apostles. That’s why the Bible calls it “the everlasting Gospel” (Revelation 14:6). In 1 Corinthians 15:3, you have Scripture’s own definition of the Gospel: the gospel is that “which you heard from the beginning” (1 John 2:24). This special message cannot be changed, redefined or added to. Note how strongly Paul makes this point in Galatians 1:8–9, where he says that it cannot be altered even by divine revelation (”an angel from heaven”).…