The article of justification, which is our only protection, not only against all the powers and plottings of men but also against the gates of Hell, is this: by faith alone in Christ, without works, are we declared righteous and saved…The article of justification is the master and prince, the lord, the ruler, and the judge over all kinds of doctrines; it preserves and governs all church doctrine and raises up our conscience before God. Without this article the world is utter death and darkness. No error is so mean, so clumsy, and so outworn, as not to be supremely pleasing to human reason and to seduce us if we are without the knowledge and contemplation of this article…This doctrine 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 short, if this article concerning Christ – the doctrine that we are justified and saved through Him alone and consider all apart from Him damned – is not professed, all resistance and restraint are at an end. Then there is, in fact, neither measure or limit to any heresy or error…Whoever departs from the article of justification does not know God and is an idolater.
– M. Luther from What Luther Says Vol. II. Ewald Pless, Translator and Editor. Concordia Publishing House, St. Louis, 1959.