Here are a couple of quotes form Luther’s Tabletalk;
All heretics have continually failed in this one point: that they do not rightly understand or know the article of justification. If we had not this article certain and clear, it would be impossible for us to criticize the pope’s false doctrine of indulgences and other abominable errors, much less be able to overcome greater spiritual errors and vexations. If we only permit Christ to be our Saviour, then we have won, for He is the only girdle which clasps the whole body together, a Saint Paul excellently teaches.
A popish priest once argued with me in this manner: Evil works are damned, therefore good works justify. I answered: Your argument is worth nothing. It concludes not ratione contrariorum; the things are not in connection. Evil works are evil in complete measure, because they proceed from a heart that is altogether spoiled and evil. But good works, yea, even in an upright Christian, are incompletely good; for they proceed out of a weak obedience but little recovered and restored. Whoso can say from his heart, “I am a sinner, but God is righteous;” and who, at the point of death, from his heart can say, “Lord Jesus Christ, I commit my spirit into your hands,” may assure himself of true righteousness, and that he is not of the number of those that blaspheme God, in relying upon their own works and righteousness.