While there is some debate as to whether or not Martin Luther said those exact words (in Latin or German, of course), it seems very clear that the doctrine of justification by faith alone is central to the Reformation. It breaks my heart to hear pastors, elders, and others who are the spiritual descendants of the Reformers treat this vital doctrine as if it doesn’t really matter all that much. Our ancestors in the faith, those in Germany, Geneva, France, England, etc., fought and died horrible deaths because they believed that Scripture clearly teaches that we are justified by faith alone, in Christ alone, by grace alone, to God alone be the glory. We must not treat our birthright so lightly.

Pastor Wes White has an excellent post with quotes from many of the Reformed Fathers on the subject of justification by faith alone. Here is an excerpt from his post:

However, as I have read classic Reformed theology, I have found that they generally did believe in a central dogma. They believed that it was justification by faith alone. This did not mean that it was a theological axiom from which all other theology was deduced. Rather, it meant:

1. That the purity of this doctrine was basic to purity in all other doctrines.
2. That any error in this doctrine was extremely dangerous.
3. That this doctrine, above all, was to be defended, explained, and meditated upon.
4. That this doctrine was the foundation of all true religion and holiness.
5. That the true Church could not be maintained without this doctrine.

In this post, I would like to demonstrate this from the writings of several different theologians from several different regions and eras.

Here is one of my favorites quotes:

Thomas Watson (1620–1686, England), A Body of Divinity, 226: “Justification is the very hinge and pillar of Christianity. An error about justification is dangerous, like a defect in a foundation. Justification by Christ is a spring of the water of life. To have the poison of corrupt doctrine cast into this spring is damnable.”

You can read the whole post here.