The Prodigal God: Recovering the Heart of the Christian Faith

A parable is a simple story used to illustrate a spiritual truth, usually by means of allegory. In the Bible, Jesus frequently employs parables to challenge his listeners’ core assumptions, and Keller argues that the Parable of the Prodigal Son is largely intended to rebuke the Pharisees’ grumbling about his welcome to sinners. The parable’s function is therefore not simply to comfort (by reassuring listeners of the father’s mercy) but to deconstruct and even offend. As the text states, “Jesus’s purpose is not to warm our hearts but to shatter our categories” (13). This power is amplified by the story’s open ending, which invites the audience of “elder brothers” to confront their condition and choose a response.

The Pharisees were one of two major branches of Judaism at Jesus’s time, the other being the Sadducees. The latter were the traditional priestly class, whereas the Pharisees emerged as a reformist sect that argued (among other things) for the importance of oral tradition alongside the written Torah. This makes the New Testament’s depiction of them as “religious insiders” somewhat ironic and ahistorical; the discrepancy may reflect the fact that their influence was more apparent in the non-elite spaces in which Jesus circulated, or it may stem from the fact that they became the dominant sect a few decades after Jesus’s death, when the New Testament was being compiled. 

Regardless, Pharisees as portrayed in the Bible typically seek righteousness through strict obedience, thus serving as the archetype for the “elder brother.” Their complaint that Jesus “welcomes sinners” provides the immediate context for the parable, establishing them as its primary audience. Keller uses this historical group to represent the modern mindset of religious moralism, which he argues is a profound form of spiritual lostness. The book contends “Jesus is pleading not so much with immoral outsiders as with moral insiders” (12), explaining why those confident in their morality were offended by radical grace.

The idea of a “prodigal” God is the book’s central concept; the word portrays God as “spendthrift” with his grace. Keller notes that the term “prodigal” implies lavish and extravagant expenditure. This provides the thesis of the book, recasting divine love as initiating, unmerited, and costly. This lavish grace is displayed in the parable when the father runs to his younger son and restores him with the best robe, a ring, and a fattened calf without demanding repentance or restitution first. This radical welcome shatters conventional religious categories, deeply offending the moralistic elder brother. Keller emphasizes that this grace, while completely free to the recipient, is infinitely costly to the giver, a cost that is ultimately paid by Jesus Christ; the idea is thus central to the theme of Costly Grace and the True Elder Brother.

Keller uses the term “self-salvation project” to denote what he describes as the universal human drive to try to secure personal worth and control over life by either rejecting God outright or seeking to manipulate him through outward compliance (thus rejecting God’s providence in spirit). This concept is central to the claim that Both Brothers Are Lost, as it unifies the siblings’ seemingly opposite strategies, revealing that their core motivation is the same: to get the father’s things without submitting to the father himself. Keller also uses the character Salieri from the play Amadeus to illustrate this dynamic, showing how a life of strict moral observance can be a transactional bargain designed to put God in one’s debt. Recognizing this underlying Sin as Self-Salvation is crucial, as it means true repentance must go deeper than confessing behavioral failures. It requires repenting of righteousness that positions a person as their own savior, a project that stands in direct opposition to the gospel’s call to trust in God’s unmerited grace.