Since the days of the early church, Christians have wrestled with the relationship between law and gospel. If, as the apostle Paul says, salvation is by grace and the law cannot save, what relevance does the law have for Christians today? By revisiting the Marrow Controversy—a famous but largely forgotten eighteenth-century debate related to the proper relationship between God’s grace and our works—Sinclair B. Ferguson sheds light on this central issue and why it still matters today. In doing so, he explains how our understanding of the relationship between law and gospel determines our approach to evangelism, our pursuit of sanctification, and even our understanding of God himself. Ferguson shows us that the antidote to the poison of legalism on the one hand and antinomianism on the other is one and the same: the life-giving gospel of Jesus Christ, in whom we are simultaneously justified by faith, freed for good works, and assured of salvation.