Shortly before his death, J. Gresham Machen wrote a brief telegram to his beloved colleague, John Murray: “So thankful for the active obedience of Christ. No hope without it.” So what is the active obedience of Christ? Why had a man like Murray held it before his friend’s heart, and why did it bring Machen such lively and solid hope? Andy Young traces the development of this doctrine, define it, and explain why it remains such a precious notion for God’s people, not only giving them confidence in life but also hope in the face of death.