What was the driving force behind the Reformation?

Joel Beeke explains in this video that the Reformation began through Martin Luther’s opposition to the selling of indulgences to release people’s souls from purgatory. Thus, it was the abuses of the Roman Catholic Church and the Papacy that initially drew the Reformers to confront these long-held practices.  

Ultimately, one of the main driving forces behind the Reformation was the issue of authority. Is Scripture sufficient for everything or does the Pope wield equal authority to Scripture? Both of them could not be the ultimate authority, for Scripture clearly contradicted the teachings of the Roman Catholic Church. 

Jeremiah 17:7-8 (NKJV) – “Blessed is the man who trusts in the Lord, and whose hope is the Lord. For he shall be like a tree planted by the waters, which spreads out its roots by the river, and will not fear when heat comes; but its leaf will be green, and will not be anxious in the year of drought, nor will cease from yielding fruit."

In terms of the Protestant Reformation, there was not a single driving idea behind it. It actually began in a more apologetic polemical mode through Martin Luther's opposition to the selling of indulgences to release people's souls from purgatory. So it was the abuses of the Roman Catholic Church and the papacy that really began the movement and that then morphed into something much more significant so that the driving force behind the Reformation soon became the whole issue of authority. Who really is in charge of this world and in charge of our lives? Is it the Scriptures?

Are they sufficient for everything? Or is the Pope a second authority source that is of equal value to the scriptures Now Rome said the latter of course Once you say that however you've got a major problem Because if the Pope says to me today that Mary, for example, is sinless, and the Bible says that Mary trusted in God her Savior, which means she was a sinner, plain and simple, which do you believe? Well, if the Pope says it, Mary sinless. I must be misinterpreting, if I'm a devout Roman Catholic, Luke 1, where Mary confesses she's a sinner. So, bottom line, papal authority supersedes scriptural authority and you see that's where early on in the Reformation by 1520 already 95 theses posted in 1517 there were major objections against that so that's one major driving force, the authority of Scripture.