Before his death on May 19, 2023, Tim Keller spent decades helping Christians think more clearly about the gospel and its implications for everyday life. One of the areas where his teaching continues to resonate is the relationship between justification by faith and sanctification.
In a thoughtful conversation with John Piper, Keller addresses several common misunderstandings Christians have about obedience, holiness, and what it actually means to live a transformed life after being saved by grace.
Their discussion is not abstract or academic. It goes straight to the heart of how Christians are motivated, why obedience matters, and how the gospel reshapes not just behavior, but desire itself.
Obedience Still Matters, but for New Reasons
Keller begins by affirming what Reformed theology has traditionally called the “third use of the law.” In simple terms, this means that even after a person is saved by grace, God’s moral law still has relevance in the believer’s life.
“I absolutely believe in what the Reformed people call the third use of the law,” Keller explains. Though Christians are saved by the gospel, they are still called to obey God. And that obedience is not merely external. God’s law presses inward, calling for inner holiness and heart change, not just outward moral behavior.
But Keller is careful to point out that the gospel radically changes why Christians obey.
Before understanding the gospel, people may try to live virtuously out of fear, self-interest, or a desire to earn approval. Keller draws on Jonathan Edwards to note that this kind of morality is still fundamentally self-centered. Even when it looks religious, it is often about what the person gets out of obedience.
The gospel, however, creates new motives.
“What the gospel does,” Keller says, “is give me profoundly new motives.”
Instead of fear or self-protection, obedience begins to flow from love, gratitude, and delight in God. Keller quotes Puritan theologian Walter Marshall, who captured this shift memorably: “You need the comforts of the gospel in order to fulfill the law.”
In other words, grace does not weaken obedience. It makes real obedience possible.
