“Martin Luther, a scholar, took quill in hand, dipped it in his inkwell and penned his 95 Theses on October 31, 1517. These were intended to spark a debate, to stir some soul-searching among his fellow brothers in the church.”

A single event on a single day changed the world. It was October 31, 1517. Brother Martin, a monk and a scholar, had struggled for years with his church, the church in Rome. He had been greatly disturbed by an unprecedented indulgence sale. The story has all the makings of a Hollywood blockbuster. Let’s meet the cast.

First, there is the young bishop—too young by church laws—Albert of Mainz. Not only was he bishop over two bishoprics, he desired an additional archbishopric over Mainz. This too was against church laws. So Albert appealed to the Pope in Rome, Leo X. From the De Medici family, Leo X greedily allowed his tastes to exceed his financial resources. So enter the artists and sculptors, Raphael and Michelangelo.

When Albert of Mainz appealed for a papal dispensation, Leo X was ready to deal. Albert, with the papal blessing, would sell indulgences for past, present, and future sins. All of this sickened the monk, Martin Luther. Can we buy our way into heaven? Luther had to speak out.

But why October 31? November 1 held a special place in the church calendar as All Soul’s Day. On November 1, 1517, a massive exhibit of newly acquired relics would be on display at Wittenberg, Luther’s home city. Pilgrims would come from all over, genuflect before the relics, and take hundreds, if not thousands, of years off time in purgatory. Luther’s soul grew even more vexed. None of this seemed right.

Martin Luther, a scholar, took quill in hand, dipped it in his inkwell and penned his 95 Theses on October 31, 1517. These were intended to spark a debate, to stir some soul-searching among his fellow brothers in the church. The 95 Theses sparked far more than a debate. The 95 Theses also revealed the church was far beyond rehabilitation. It needed a reformation. The church, and the world, would never be the same.

One of Luther’s 95 Theses simply declares, “The Church’s true treasure is the gospel of Jesus Christ.” That alone is the meaning of Reformation Day. The church had lost sight of the gospel because it had long ago papered over the pages of God’s Word with layer upon layer of tradition. Tradition always brings about systems of works, of earning your way back to God. It was true of the Pharisees, and it was true of medieval Roman Catholicism. Didn’t Christ Himself say, “My yoke is easy and my burden is light?” Reformation Day celebrates the joyful beauty of the liberating gospel of Jesus Christ.

What is Reformation Day? It is the day the light of the gospel broke forth out of darkness. It was the day that began the Protestant Reformation. It was a day that led to Martin Luther, John Calvin, John Knox, and may other Reformers helping the church find its way back to God’s Word as the only authority for faith and life and leading the church back to the glorious doctrines of justification by grace alone through faith alone in Christ alone. It kindled the fires of missionary endeavors, it led to hymn writing and congregational singing, and it led to the centrality of the sermon and preaching for the people of God. It is the celebration of a theological, ecclesiastical, and cultural transformation.

So we celebrate Reformation Day. This day reminds us to be thankful for our past and to the Monk turned Reformer. What’s more, this day reminds us of our duty, our obligation, to keep the light of the gospel at the center of all we do.

This article first appeared on Ligonier.org, and is used with permission.