Early in his life, while he was an Augustinian monk, Luther slowly came to realize that there is nothing we can do to be set right with our most holy Creator. In fact, as he confessed sin and read Scripture, he came to understand that no fallen person could have any hope of salvation if, in fact, divine forgiveness depends on a sinner’s obedience to the law of God.
Besides Luther’s existential struggle with his guilt, we can see other events in which God was working providentially to show him the gospel of Christ’s sufficient work in behalf of His people. In 1510, Luther traveled to Rome to represent his monastery before the Vatican, and was shocked by the debauchery and licentiousness he saw in what was supposed to be a holy city. Priests were engaged in flagrant prostitution, homosexuality, and hypocrisy, prompting Luther to question many of the non-biblical traditions embraced in the medieval church.
All of these things — Luther’s existential guilt, the church’s moral failings, and his study of Scripture — came to a head in 1515. While lecturing through Psalms and Romans that year as a professor of theology, Luther finally saw that he could be forgiven and that he could find peace with God based on the righteousness of Jesus, which the Lord would credit to his account if he would abandon his attempt to earn his own righteousness and trust in Jesus alone (Rom. 3:21–22a).
Luther slowly grew in his understanding that Christ’s work is sufficient to meet the sinner’s need for forgiveness. In 1517, the crass sale of papal indulgences moved Luther to nail the Ninety-Five Theses to the Castle Church door in Wittenburg. This document of protest against the abuses of the medieval church was intended to provoke academic debate about indulgences in the isolated town of Wittenburg, but others copied the theses and distributed them throughout Germany.
The pope did not take kindly to Luther’s protest, especially when the study of other Reformers also showed the insufficient biblical basis for all manner of medieval church traditions. But Luther and these other men could stand firm despite threats of death because they understood the sufficiency of Christ, that He was all they needed in life and death. And so the reformation of the church began.