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.
Source: What Is Reformation Day?