In 2007, The Gospel Coalition asked John Piper “What is the gospel?”

His answer:

1. A plan 
2. An event 
3. An achievement 
4. An offer 
5. The application 
6. God

Watch Piper's explanation:

And consider attending The Gospel Coalition’s 2011 National Conference on “They Testify About Me: Preaching Jesus and the Gospel from the Old Testament" in Chicago April 12-14.