Today is Reformation Day, a watershed day in human history and church history. The Reformers restored to the church God's precious gifts, the Bible and grace, that had been usurped by church claims to authority. It marked a great change in the church that affects every single Christian life today. It's a day I think all Christians should mark and be thankful for because our lives, our relationship with Christ, would be very different if it had never happened.
The principles Martin Luther raised when he nailed the "95 Theses" on the church door are fundamental to Christianity today, the way we think about our relationship with God. The Bible is our authority for God's revelation and doesn't have to be mediated by the church authorities. Salvation is a free gift of God as an act of grace received by faith, and we can be confident in that hope; it's not merited by works. We can have direct access to God and we are all equal before Him.
The Reformation sparked lasting change in Christianity and in the world. Other reformers carried on the change Luther sparked and the world was changed forever.