Ephesians 2:8-9

For by grace are ye saved through faith; and that not of yourselves: it is the gift of God:
Not of works, lest any man should boast

This verse shows why the Popes in the time of the Renaissance practically hid part of the Word of God from the common people. The result of them finding out the truth about salvation through faith ( and other doctrine) would hinder the power of the Popes, among other problems. Martin Luther (above) is admired by many of his bravery of standing up to these powerful Popes by confidently posting his "95 Theses" that contained major problems with the Catholic religion to the door of the Wittenberg Castle Church in Germany. He started one the most important times in history that is well remembered. Even though Luther may not have had everything correct in his doctrinal beliefs, we can certainly follow his example of his courage and determination to do what's right. Of course, there is much more to his story, but I think his Thesis is something everyone should know about. 

-picture from google images-