From Roland Bainton's biography of Martin Luther, Here I Stand, today's quote comes from the great turning point in Luther's life in 1515--when he grasped the meaning of justification by faith in Paul's letter to the Romans.
I greatly longed to understand Paul's Epistle to the Romans and nothing stood in the way but that one expression, "the justice of God," because I took it to mean that justice whereby God is just and deals justly in punishing the unjust. My situation was that, although an impeccable monk, I stood before God as a sinner troubled in conscience, and I had no confidence that my merit would assuage him. Therefore I did not love a just and angry God, but rather hated and murmured against him. Yet I clung to the dear Paul and had a great yearning to know what he meant.
Night and day I pondered until I saw the connection between the justice of God and the statement that "the just shall live by his faith." Then I grasped that the justice of God is that righteousness by which through grace and sheer mercy God justifies us through faith. Thereupon I felt myself to be reborn and to have gone through open doors into paradise. The whole of Scripture took on new meaning, and whereas before the "justice of God" had filled me with hate, now it became to me inexpressibly sweet in greater love. This passage of Paul became to me a gate to heaven.