Luther on Justification:
"The first and chief article is this: Jesus Christ, our God and Lord, died for our sins and was raised again for our justification (Romans 3:24-25). He alone is the Lamb of God who takes away the sins of the world (John 1:29), and God has laid on Him the iniquity of us all (Isaiah 53:6). All have sinned and are justified freely, without their own works and merits, by His grace, through the redemption that is in Christ Jesus, in His blood (Romans 3:23-25). This is necessary to believe. This cannot be otherwise acquired or grasped by any work, law or merit. Therefore, it is clear and certain that this faith alone justifies us ... Nothing of this article can be yielded or surrendered, even though heaven and earth and everything else falls (Mark 13:31)." [Luther, Martin. "The Smalcald Articles," in Concordia: The Lutheran Confessions. (Saint Louis: Concordia Publishing House, 2005, 289, Part two, Article 1.]
Here is another great quote from Luther on spiritual warfare provided by my pastor, Akash Sant Singh:
"If I profess with the loudest voice and clearest exposition every portion of the truth of God except precisely that little point which the world and the devil are at that moment attacking, I am not confessing Christ, however boldly I may be professing Christ. Where the battle rages, there the loyalty of the soldier is proved, and to be steady on all the battlefields besides that one, is mere fight and disgrace if he flinches at that point." -Martin Luther
The 95 Theses - Read Luther's words that helped create the protestant churches of today.