I just recently read and completed this book. Its main thesis is that the Gospel is not something believers should “move on” from after conversion. Instead, Christians should seek to grow in deeper love with the Gospel everyday and allow its reality to affect every aspect of who they are and the way they live. This excerpt from the book seems to summarize its main theme rather well:
I can hear you asking, ‘But don’t I need more than the cross?’
In one sense, the answer is no. Nothing else is of equal importance. The message of Christ and Him crucified is the Christian hope, confidence, and assurance. Heaven will be spent marveling at the work of Christ, the God-Man who suffered in the place of us sinners.