Human beings have not kept the law of God but have transgressed it. Their corrupted human nature, thoughts, words, and deeds battle against the law. For this reason they are subject to God’s wrath, to death and all temporal afflictions, and to the punishment of the fires of hell. As a result, the Gospel, in its strict sense, teaches what people should believe, namely, that they receive from God the forgiveness of sins; that is, that the Son of God, our Lord Christ, has taken upon Himself the curse of the law and borne it, atoned and paid for all our sins; that through Him alone we are restored to God’s grace, obtain the forgiveness of sins through faith and are delivered from death and all the punishments of our sins and are saved eternally. . . . It is good news, joyous news, that God does not want to punish sin but to forgive it for Christ’s sake (Formula of Concord: Solid Declaration, V:20).
That is how the Lutheran Confessions explain what the Gospel is all about. I really like this quote. Short, simple, to the point. This is a great summary of the Gospel and the heart of the Reformation.