What was one of the most important doctrines of the Reformation?

Anthony Mathenia explains in this video that the Reformation was important then and continues to be important today because it introduced the doctrine of justification by faith. Churches today have departed from this issue that there is a holy and just God and that we justly deserve His condemnation and judgment if we do not repent and believe the Gospel. 

If justification by faith does not remain a central aspect of our lives, then we will find ourselves in need of a massive reformation in our homes and lives. 

Romans 5:1 (NKJV) – “Therefore, having been justified by faith, we have[a] peace with God through our Lord Jesus Christ.”

One of the ways that the Reformation is still of crucial importance in our lives today is justification by faith. It's not just an old doctrine that was good for the Apostle Paul or that was good for Martin Luther. But churches in our day across the globe have unfortunately gotten away from this crucial, important issue that there is a holy, just, and righteous God that we as sinners have offended and we are due his righteous wrath. His anger is against us. Condemnation is hanging over us if we do not repent and believe the gospel.

If justification by faith does not remain a central aspect of our gospel, of our lives, of our families, of our churches, then we will find ourselves again like our spiritual fathers before in need of a massive reformation within the church, within the home, and within our lives. You