What is the gospel? How would you define it in a single sentence? This question gets bantered around quite a bit and there is more than one way to truthfully answer it. Here's an attempt that I found particularly helpful.
“The essence of the Christian religion consists in this, that the creation of the Father, devastated by sin, is restored in the death of the Son of God, and re-created by the Holy Spirit into a kingdom of God.”
This is from Herman Bavinck's Reformed Dogmatics. Bavinck was a nineteenth-century Dutch neo-Calvinist theologian who left an incredible four-volume systematic theology which has only recently been fully translated into English. I'm spot-reading in it and so found this quote.
Here's what I like about it.
2. It captures the story-line of Scripture - notice creation ("creation of the Father"), fall ("devasted by sin"), redemption ("restored in the death of the Son of God"), and new creation ("re-created by the Holy Spirit into a kingdom of God.").
3. It is cross-centered - "restored in the death of the Son of God." I think it would be better to also add the resurrection and say "restored in the death and resurrection of the Son of God." But I am glad that the death of Christ is not minimized, but is front and center.
4. It is kingdom-oriented - "re-created by the Holy Spirit into a [should we say "the"] kingdom of God."
5. It is short.
Good stuff. Gotta love those Dutch folks!