I've just read a statement that makes so much sense of "the gospel". Today we often hear words sadly confused. For example, people often talk about evangelism when they mean evangelicalism. So I offer this thought from Tom Wright's "Surprised by hope".

So let's start with the latter point, and say clearly at once: 'the gospel', in the New Testament, is the good news that God (the world's creator) is at last becoming king, and that Jesus, whom this God raised from the dead, is the world's true Lord.