Martin Luther asked several theological questions related to the nature of salvation. Two of the most fundamental are "How can I be assured of my salvation?" and "What is the 'justice of God?'" Luther believed the Catholic Church promoted a works-based approach to salvation. No matter how much he confessed, he always feared he had forgotten about some of his sins and would be condemned. Eventually--through his study of Paul's Epistles--Luther began to believe salvation came not through works but by faith. As Galatians 3:11 (English Standard Version) expresses:
Now it is evident that no one is justified before God by the law, for “The righteous shall live by faith.”
Luther's interpretation of Catholic teachings on salvation also caused him to question the meaning of the "justice of God." He could not understand how a wretched sinner such as himself could make himself acceptable before a holy God, which caused him to hate "this just God who punishes sinners." However, once Luther began to believe that salvation came through faith, not works, he recognized the role which grace plays in God's justice. As historian Jackson Spielvogel says in Western Civilization, "To Luther, the 'justice of God' was now not a punitive justice but the grace of God that bestows salvation freely to humans...through the sacrifice of Christ on the cross" (page 461).