A story goes that Martin Luther visited Rome at a time Latin was the language of the clergy and the Bible. His visit was to reaffirm his faith in the church as a whole.
There, in St. Peter's Cathedral, priests would hold small masses throughout the cathedral throughout the day. Martin Luther overheard these masses only to discover that priests were having personal conversations with each other in Latin, faning mass. Martin Luther wrote to the Papacy who disregarded his letter, overwhelming Luther with the corruption in the Roman Catholic Church.
This only heightened Luther's already strong conclusion that the teachings of the church were not in concert with the scriptures. Eventually Luther would come to the conclusion that the church was in error and would bring about the Reformation, an effort only intended to pruify the Roman Catholic Church, not to bring about what we today call Protestantism.
Luther's Reformation included three key teachings:
sola gratia (Grace Alone)
That is, salvation itself is only possible as a result of God's grace. This is relevant in Luther's time and our own as it addresses that no one can "earn" their way to heaven through good works. By the grace of God alone can man be saved.
sola fide (Faith Alone)
In light of not earning our way into heaven, then by what action can man be saved? Faith Alone confirms Grace Alone in that man can do no work, but only through faith in God can he receive God's gift of salvation.
sola scriptura (Scripture Alone)
Again relevant in Luther's and our own time, Scripture Alone speaks to what has final authority in the arbitration of doctrine. Scripture Alone does not discredit other sources of guidance such as Revelation and Counsel, but Sola Scriptura declares that the Bible's authority trumps that of any other.