Jerry Bridges is one of the great Christian authors of our day. Below he answers the question, "How would I state the gospel in 30 seconds or less?"
Bridges cites 1 Corinthians 15:1-3.
 Now I would remind you, brothers, of the gospel I preached to you, which you received, in which you stand,  and by which you are being saved, if you hold fast to the word I preached to you—unless you believed in vain.
 For I delivered to you as of first importance what I also received: that Christ died for our sins in accordance with the Scriptures . . . 1 Corinthians 15:1-3.