In 1519 Luther had his famous 'Tower Experience' in which he discovered the true meaning of righteousness.
Meanwhile in that same year, 1519, I had begun interpreting the Psalms once again. I felt confident that I was now more experienced, since I had dealt in university courses with St. Paul's Letters to the Romans, to the Galatians, and the Letter to the Hebrews. I had conceived a burning desire to understand what Paul meant in his Letter to the Romans, but thus far there had stood in my way, not the cold blood around my heart, but that one word which is in chapter one: "The justice of God is revealed in it." I hated that word, "justice of God," which, by the use and custom of all my teachers, I had been taught to understand philosophically as referring to formal or active justice, as they call it, i.e., that justice by which God is just and by which he punishes sinners and the unjust.
But I, blameless monk that I was, felt that before God I was a sinner with an extremely troubled conscience. I couldn't be sure that God was appeased by my satisfaction. I did not love, no, rather I hated the just God who punishes sinners. In silence, if I did not blaspheme, then certainly I grumbled vehemently and got angry at God. I said, "Isn't it enough that we miserable sinners, lost for all eternity because of original sin, are oppressed by every kind of calamity through the Ten Commandments? Why does God heap sorrow upon sorrow through the Gospel and through the Gospel threaten us with his justice and his wrath?" This was how I was raging with wild and disturbed conscience. I constantly badgered St. Paul about that spot in Romans 1 [Romans 1:17] and anxiously wanted to know what he meant.
I meditated night and day on those words until at last, by the mercy of God, I paid attention to their context: "The justice of God is revealed in it, as it is written: 'The just person lives by faith.'" I began to understand that in this verse [Romans 1:17] the justice of God is that by which the just person lives by a gift of God, that is by faith. I began to understand that this verse means that the justice of God is revealed through the Gospel, but it is a passive justice, i.e. that by which the merciful God justifies us by faith, as it is written: "The just person lives by faith." All at once I felt that I had been born again and entered into paradise itself through open gates. Immediately I saw the whole of Scripture in a different light. I ran through the Scriptures from memory and found that other terms had analogous meanings, e.g., the work of God, that is, what God works in us; the power of God, by which he makes us powerful; the wisdom of God, by which he makes us wise; the strength of God, the salvation of God, the glory of God.
I exalted this sweetest word of mine, "the justice of God," with as much love as before I had hated it with hate. This phrase of Paul was for me the very gate of paradise. Afterward I read Augustine's "On the Spirit and the Letter," in which I found what I had not dared hope for. I discovered that he too interpreted "the justice of God" in a similar way, namely, as that with which God clothes us when he justifies us. Although Augustine had said it imperfectly and did not explain in detail how God imputes justice to us, still it pleased me that he taught the justice of God by which we are justified.
Notice how when Luther came to understand the Gospel in Romans 1 his insight was bolstered by the fact that he was able to verify his conclusion with the rest of Scripture from memory. He immediately knew that his interpretation agreed with the rest of the Bible.