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.
In another sense, the answer’s yes. You do need more. You’ve been saved to grow, to serve in a local church, to do good works, and to glorify God. But the ‘more’ you need as a follower of Christ won’t be found apart from the cross. The Gospel isn’t one class among many that you’ll attend during your life as a Christian–the gospel is the whole building where all the classes take place! . . .
Name any area of the Christian life that you want to learn about or that you want to grow in. . . . None of these can be rightly understood apart from God’s grace through Jesus’ death. They, and indeed all topics, should be studied through the lens of the gospel.
As you may have picked up, this book is not an academic book for those living in ivory towers. It’s very down to earth. It’s very practical. But it’s also very rich and theological. In short, What Mahaney does in this book is meditate on the Gospel, describe the Gospel, explain the basic theology of the Gospel and its implications to sinners, and then show how the Gospel is the solution to the various problems we as Christians tend to gravitate towards (i.e., legalism, condemnation, emotionalism/subjectivism, etc.)
I closing, this book is not intimidating whatsoever–a very small book, a very short read, and very understandable. But its truths are profound. I highly recommend it.
Mahaney applies the Gospel to some very common problem areas for Christians, but he certainly does not exhaust the issue–more can definitely be said.