What was a driving force behind the Reformation?

Joel Beeke explains in this video that one major driving force behind the Reformation was the doctrine of justification by faith alone. Once Luther, Calvin, and the other Reformers grasped hold of the doctrine of justification by faith alone, the Roman Catholic Church’s false teachings were exposed. A person's supposed "good works" could never save a sinner. 

The Reformation soon became known as a reformation of grace alone - that grace alone saves us. While we are sanctified and cooperate with the Spirit in our sanctification, there is never any credit due to us or anything we that must do to "earn" our salvation. We are saved by God’s grace alone.  

Ephesians 2:8-9 (NKJV) - "For by grace you have been saved through faith, and that not of yourselves; it is the gift of God, not of works, lest anyone should boast."

And then the third major driving force was, of course, the historic doctrine of justification by faith alone. That's really what broke Luther's soul, as he said, broke it open for the gospel, and his heart, as it were, was taken away to paradise when he saw that God was righteous, but it was righteousness through faith in the Lord Jesus Christ. And so once Luther, and then later, of course, Calvin and the other reformers, once they grasped hold of this, that were justified by faith alone, that then exposed the whole Roman Catholic synergism in all areas of doctrine so that the Reformation became known by this little word alone, or saved by grace alone rather than grace and works, or justified by faith alone rather than faith and works. It's the glory of God alone that's at stake rather than the glory of God and the church and It's the scripture alone rather than scripture and tradition so that's how it evolved and the Reformation soon became known as a reformation of grace. That grace alone saves us.

Yes, we do go to work. Yes, we are sanctified. Yes, we cooperate with the Spirit in our sanctification, but never any credit to us. It's always God's grace in our justification and it's God's grace even when we're sanctified. So the end result is that the corruptions of the papacy, the moral corruptions of the Church, the anger of the populace at the Church's abuses, all were motivating forces but ultimately the driving ideas are authority and scripture and faith alone.