Prodigal God by Tim Keller takes an in-depth look at the famous story of the "prodigal son" in Luke 15. Keller does an excellent job of showing how believers are often both the younger and older brother in the story. Keller ultimately shows us that the gospel is neither mere religion nor irreligion but centers on grace, which is lavished on us by the love of the Father. This is one of the best books by the late Tim Keller, and I pray it serves you well by reminding you of the preciousness of grace.
There are a few copies available to purchase from the Bookstall for $10 each or order on AMAZON