What is the Gospel?

Yesterday I began reading Greg Gilbert's What is the Gospel? It begins, "You'd think that would be an easy question to answer, especially for Christians. In fact, you'd think that writing a book like this--one asking Christians to think carefully about the question, What is the gospel of Jesus?--would be completely unnecessary. It's like asking carpenters to sit around and ponder the question, What is a hammer?"

And yet as unnecessary as this question should be, it's being asked. And answered. And the answer to this question either provides answers to all the other important questions or it raises other questions with which its answers are less than satisfying. In my preaching and teaching I've tried to answer this question, as this is the main purpose of preaching and teaching the Word of God, though I have not always articulated it so clearly. So perhaps my own understanding of the Gospel could use some work. Thus the read. As I read, I hope to interact with and articulate Gilbert's book but more importantly interact and articulate what the Gospel is (or isn't.)