On October 31, 1517, a Roman Catholic monk named Martin Luther knocked on an old wooden door, but he wasn't looking for Halloween candy. However, he scared the snot out of quite a few people, particularly the leadership of the church, with his 95 thesis that he tacked on the door of the church in Whittenburg, Germany.
You see, what was scary to them was Luther's rediscovery of the truth of the word of God, particularly the doctrine of justification by grace through faith in Jesus Christ alone. To Catholic ears, this sounded (and still sounds) like so much nonsense. To the ears of a Christian, it sounds like freedom.
Let's all pray for the courage to stand up for the truth of God's word like Martin Luther. Praise God for the Reformation.