"But the righteous shall live by his faith."
Martin Luther, made a life changing discovery involving this verse. For his entire life as a Catholic monk in a monastery, he was told that "the righteous shall live by faith". Being fully devout, Luther tried his hardest to live by faith in order that he may be righteous, but try as he might he could never seem to confess enough sins or do enough penance to ever truly feel forgiven. He confessed so often and so many things, his confessor grew tired of him and told him to "come back when you have something to really confess."
Luther was stuck in the cycle of despair. No matter how hard he tried to live by faith, he always fell short of righteousness. Until, that is, he read this verse quoted by Paul in Romans 1:17 in the original Greek. He realized for the first time that it is not living by faith which makes us righteous, but rather it is faith which makes us righteous so that we will live. The act of sanctification, though once active to Luther, became passive, that is, the righteousness is already ours if we believe.
Luther went back to the works of his favorite Church Father, Augustine, and it was just as he had hoped. Suddenly, the burden of being a Christian was lifted from him, perhaps leading to the Reformation. Finally he felt forgiven. Finally he felt the innumerable joy of grace. Finally, he was free.