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.
Better armed now with these thoughts, I began for the second time to interpret the Psalms. The work would have grown into a large commentary, but I was summoned the following year to Worms for the Diet convened by Emperor Charles V and so had once again to leave the work I had begun.
I am telling you all this, dear reader, so that, if you are going to read my little works, you should remember that I am one of those, as I said above, who, as Augustine writes of himself, makes progress by writing and teaching. I am not one of those who out of nothing suddenly become perfect (although in fact they are nothing), who don't work, who aren't tempted, who have no experience, but who, with one look into the Scriptures, exhaust their whole spirit.
Up to that point, 1520-21, the indulgence affair was still going on. There followed the affairs dealing with the sacraments and with the Anabaptists, about which I will write prefaces in other volumes, if I live to do so.
Good-bye in the Lord, dear reader, and pray that the word may increase against Satan, because he is powerful and evil. And now he has become extremely vicious and savage because he knows that he has only a short time and that the kingdom of his pope is endangered. May God strengthen in us what he has accomplished. May he prosper his work which he has begun in us for his glory [cf. Phillipians 1:6 and Psalm 68:29]. Amen.
Source of English translation (from the Latin original): Martin Luther, “Preface to the Complete Edition of Luther’s Latin Works,” translated by Bro. Andrew Thornton. © 1983 by Saint Anselm Abbey. Full text available online at Project Wittenberg.