What is the Protestant belief known as "faith alone"?

"Faith Alone"? -------------- If you have heard the term "Protestant" before, chances are you have also heard the saying "faith alone." The way Protestants speak of "faith alone" might almost give one the impression that Luther and his band of rebels chanted this mantra all the way out of the Catholic cathedral as they defected from the Mother Church and set off to seek a better way. So what is the story on this "faith alone" concept? As a Protestant, the first place I go when I have questions is Scripture. ("Sola Scriptura," right?) When I do a query in the NASB Bible on "faith alone" this is the only entry that comes up: > You see that a man is justified by works and **not by faith alone**. ***-James 2:24*** That is humorous. *(Of course, from what I am told, Luther did not believe that the book of James belonged in the canon of Scripture anyway... but I digress.)* So where did the idea of "faith alone" come from? From what I understand , Luther had translated the following verse into Latin, at which point the Catholic church back-translated it into German, incorrectly rendering the bolded term as "faith alone": > For we maintain that a man is justified by **faith** apart from works of the Law. ***-Romans 3:28*** So the Catholics rendered the Latin as "**faith alone** apart from works of the Law," and were outraged. However, Luther maintained that the Catholics had mistranslated his Latin, and that the Latin *solum* ("alone") was necessary **in Latin** to convey the meaning of the sentence, though they were correct that the extra term was unnecessary in German. So in Luther's mind, the Latin was accurate **with** *solum* ("alone"), and the German was accurate **without** *allein* ("alone"). **All that to say it seems that in Luther's mind "faith alone" was nothing more than a Catholic mistranslation! *So how did it become a Protestant mantra?!*** To further complicate matters, Romans 3:28 does not contrast faith with ***works***, but with ***works of the Law***; i.e. the Mosaic Law. Yet the modern Protestant mantra seems to contrast faith with ***any sort of action.*** My Question ----------- So, can someone explain the Protestant doctrine of "faith alone" to me? Do I have my facts straight about its origin (a Catholic mistranslation from Latin to German)? If so, how in the world did a Catholic mistranslation (that Luther rejected) become a Protestant mantra?! Also, is this doctrine really as foundational to Protestantism as people think it is? And what does this doctrine even ***mean***? Is it "faith apart from any action"? Is it "faith apart from the Mosaic Law"? Something else? Would Luther even affirm the Protestant doctrine of "faith alone"? -------------- *Related: What is the biblical basis for salvation by faith alone (sola fide)? This question asks how a person would justify this doctrine from Scripture. It's not the same as what I'm asking here, but it is relevant none the less.* *Also related: Can someone help me cite Luther's explanation of faith alone to Catholics ? This question asks for a particular source to use in an upcoming blog post. Not at all what I'm asking, but related none the less.*