It seems that Martin Luther is quoted on every subject from economics to sexuality. Perhaps that is a good approach for this question as well. There are two very famous quotes attributed to Marten Luther that sum up what his greatest impact was. First at his trial in 1521 Luther is quoted as saying “Unless I am convicted by scripture and plain reason – I do not accept the authority of the popes and councils, for they have contradicted each other – my conscience is captive to the Word of God. I cannot and I will not recant anything for to go against conscience is neither right nor safe. God help me. Amen.” Luther is literally going against how Christians had thought for almost 1000 years. By taking the authority out of the hands of the Church and placing it solely on scripture Luther was, though I doubt he knew it, setting in to motion events that would shape how we think today. Prior to this the Church interpreted the bible and told the people what to believe, but that did not fly with Luther. The second quote is “This doctrine [justification by faith] is the head and the cornerstone. It alone begets, nourishes, builds, preserves, and defends the church of God; and without it the church of God cannot exist for one hour….” In this quote we see the formation of the reformation. Justification by faith became the battle cry of the reformers. With the first statement Luther removed the Churches authority to tell the people how to read scripture and with the second Luther took the power of salvation out of church membership. The doctrine of justification by faith is so far reaching it is hard to accurately sum it up, however, one thing that can be said for it is that the people now understood that they were now free to be saved without church membership. This means they could and would have to truly seek out truth and that is an undertaking the start with Luther and continues until this day.
Selected from What Luther Says, an anthology compiled by Edwald M. Plass, Vol.2, pp.702-704, 715-718.