The Protestant Reformation led to many successful innovations that never would of been able to be produced if the Roman Catholic Church remained the authority of Christian faith. The reformers preached religious freedom from the Papacy, and began preaching and teaching the Bible outside of the Roman Catholic Church's authority. Christians who followed the reformers were called "Protestants" and went on to bring forth world changing innovations for God's glory. Reformers brought forth the printing press invention, which unleashed mass printing of the Scriptures and Christian literature. Reformers translated the Bible so the common people of their lands could read the Scriptures. Probably one of the coolest things that came out of the Reformation was a regenerated church that emphasized biblical evangelism, missions, and discipleship that was non-existent for almost a thousand years.
The reformers taught the Word of God and established the "Five Solas" as their fundamental theological set of beliefs directly opposite of the Roman Catholic Church. The Latin word sola means "alone" or "only" in English. The Five Solas are: (1) Sola scriptura ["by Scripture alone"], (2) Sola fide ["by faith alone"], (3) Sola gratia ["by grace alone"], (4) Solus Christus or Solo Christo ["Christ alone" or "through Christ alone"], (5) Soli Deo gloria ["glory to God alone"].
It is important to remember Reformation Day every year because it reminds us of the importance of getting the gospel correct (cf. Galatians 1:6-8), and make a priority to preach to all nations the bloody cross gospel (cf. 1 Corinthians 2:2).