What is the Gospel? According to 1 Corinthians 15:1-4, the Gospel is embodied in these words: "Moreover, brethren, I declare unto you the gospel which I preached unto you, which also ye have received, and wherein ye stand; By which also ye are saved, if ye keep in memory what I preached unto you, unless ye have believed in vain. For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures; And that he was buried, and that he rose again the third day according to the scriptures."
1 Corinthians 2:2 says, "For I determined not to know any thing among you, save Jesus Christ, and him crucified."
John Piper said, "The Gospel is not just a sequence of steps (say, the ‘Four Laws’ of Campus Crusade or the ‘Six Biblical Truths’ of Quest for Joy ).Those are essential. But what makes the Gospel ‘good news’ is that it connects a person with the ‘unsearchable riches of Christ.’ There is nothing in itself that makes ‘forgiveness of sins’ good news. Whether being forgiven is good news depends on what it leads to. You could walk out of a courtroom innocent of a crime and get killed on the street. Forgiveness may or may not lead to joy. Even escaping hell is not in itself the good news we long for -- not if we find Heaven to be massively boring."