In his Theology of the Reformers, Timothy George recounts, through Luther’s own words, the seminal discovery that changed church history and the world as we know it:
Near the end of his life, Luther remembered how as a monk the phrase “justice of God” in Rom 1:17 had struck terror in his soul. All of his attempts to satisfy God–his prayers, fastings, vigils, good works–left him with a wholly disquieted conscience. His mood swung from despair over his own failures to a simmering rage at God: “I did not love, indeed I hated, that God who punished sinners; and with a monstrous, silent, if not blasphemous, murmuring I fumed against God.” Still, he “knocked persistently upon Paul,” meditating day and night in his study in the tower, until
I began to understand that the “justice of God” meant that justice by which the just man lives through God’s gift, namely by faith. This is what it means: the justice of God is revealed by the gospel, a passive justice with which the merciful God justifies us by faith, as it is written: “He who through faith is just shall live.” Here I felt that I was altogether born again and had entered paradise itself through open gates.