"The Prodigal God" is a book by Tim Keller that explores the parable of the Prodigal Son from the Bible. Keller emphasizes the themes of grace, forgiveness, and the nature of God as a loving father. He argues that both the younger and older sons represent different ways people can distance themselves from God. The book highlights how the term "prodigal" means wasteful, referring not only to the son's reckless spending but also to God's extravagant grace. Keller invites readers to reconsider their understanding of Christianity and the depth of God's love for all, regardless of their past actions.