There are few lessons from the Reformation that stand more clear then the lesson of "Sola Scriptura." As you read about the reformers, there is one characteristic that accompanies each of them. They valued the authority of scripture over the assumed authority of the Pope and the tradition of the church.
Sola Scriptura: the belief that the Scripture alone is the final and only infallible source for matters of faith and practice.
Why was this important?
Scripture is clear that the heart of every man is desperately wicked and unchecked, can corrupt everything that men put their hands to. This means that when men are given absolute authority it inevitably leads to error. In the case of papal authority in the era of the reformation, the authority of the Pope led to un-biblical practices such as; salvation through penance, the punishment of purgatory, the selling of indulgences, and the assumed civil authority of the church.
It was important to recognize and teach that Scripture has final authority over and above the ideas and traditions of men, because in scripture we find the very words of God Himself. If the church were to follow man into erroneous ideas, the church may be found acting in direct defiance before God. If is prudent and right to God's word to have first authority in the life of the church and in the life of every believer.
How does it affect us now?
We believe today, just as the reformers did, that we possess the very words of God. This has far reaching impact for every believer; at all times. If we possess the very words of God than we must treat them as precious and worthy of our attention and submission.