When confronted with the great Psalm 51 and its main themes of repentance and justification, Luther felt that he was truly a student who needed the Holy Spirit as his schoolmaster. Nevertheless, his commentary may be called a masterpiece. Luther's modesty came from the fact that it was impossible for a human to understand what sin, grace, and true repentance were; this had to be given by God. Because the papacy had not understood sin as an evil root and a sickness unto death, it was also unable to understand grace. Therefore, Luther could not limit himself to a mere commentary, but also had to argue against this false view. It is not by chance that in this context we find Luther's tersest definition of theology: "The knowledge of God and of man is divine wisdom and true theology. And it is the knowledge of God and of man that is ultimately related to the God who justifies and to man the sinner, so that the subject of theology is really man who is guilty and lost and the God who justifies and who is the Savior." Anything in theology that is more than this is an error and worth nothing at all. It really has to do with the eternal fate of man. But by the God who shows mercy Luther means no one but the Christ who gives his promise. He, and not the judge, as the whole tradition had said, is the righteous God. This was the bridge over the deep chasm between God's righteousness and his mercy. Contrary to all expectations, the sinner could plead for mercy. The Christian life consisted of nothing but grace. Everything depended on whether one thought of God as vengeful or as merciful, for he would meet man accordingly. To lose oneself in the depths of grace "is our true theology." God had nothing to do with saints; a "holy man" was a fiction. Even after a gracious God had forgiven him, a Christian needed God's help in his daily struggle against sin. External crosses and dangers thus were some of the means that the Holy Spirit used to train Christians.
Man's sinfulness was not in his deeds. On the basis of Ps. 51:7, it was part of his elemental nature. However, Luther was cautious not to ascribe a special taint to marriage, procreation, and conception. The original sinfulness of man was ultimately a mystery, although it was a primary theological statement without which the Holy Scriptures could not be understood. But God loved those who acknowledged that they were lost. He purified them and set them free. "God is no other than the one who loves the contrite, the tormented, the perplexed, the God of the humble. If I could understand this, I would be a theologian." Anyone who came to God in a lost conodition brought him the most appropriate offering. However, it was difficult to turn from this lost condition to trusting in God; this was the "true theology." In contrast to the preceding lectures, the exposition of Psalm 51 dealt hardly at all with the contemporary situation. It concentrated completely on the real concern of theology, the God who was gracious to the sinner, As Luther had really done ever since his decisive discovery. (pp. 456-457)
It would be nice to find a link to this commentary. It sounds very worth reading.
In the meantime, and it being Lent, we can contemplate what it means to bring a real sinner to our merciful God, who is to be thanked and praised for his undeserved kindness for such as each of us.
"The Christian life consisted of nothing but grace. Everything depended on whether one thought of God as vengeful or as merciful, for he would meet man accordingly. To lose oneself in the depths of grace "is our true theology."-- Wow.
(... I can't find the commentary on-line. But we do have Psalm 51, itself!)
For the director of music. A psalm of David. When the prophet Nathan came to him after David had committed adultery with Bathsheba.
1 Have mercy on me, O God,
according to your unfailing love;
according to your great compassion
blot out my transgressions.
2 Wash away all my iniquity
and cleanse me from my sin.
3 For I know my transgressions,
and my sin is always before me.
4 Against you, you only, have I sinned
and done what is evil in your sight;
so you are right in your verdict
and justified when you judge.
5 Surely I was sinful at birth,
sinful from the time my mother conceived me.
6 Yet you desired faithfulness even in the womb;
you taught me wisdom in that secret place.
7 Cleanse me with hyssop, and I will be clean;
wash me, and I will be whiter than snow.
8 Let me hear joy and gladness;
let the bones you have crushed rejoice.
9 Hide your face from my sins
and blot out all my iniquity.
10 Create in me a pure heart, O God,
and renew a steadfast spirit within me.
11 Do not cast me from your presence
or take your Holy Spirit from me.
12 Restore to me the joy of your salvation
and grant me a willing spirit, to sustain me.
13 Then I will teach transgressors your ways,
so that sinners will turn back to you.
14 Deliver me from the guilt of bloodshed, O God,
you who are God my Savior,
and my tongue will sing of your righteousness.
15 Open my lips, Lord,
and my mouth will declare your praise.
16 You do not delight in sacrifice, or I would bring it;
you do not take pleasure in burnt offerings.
17 My sacrifice, O God, is[b] a broken spirit;
a broken and contrite heart
you, God, will not despise.
18 May it please you to prosper Zion,
to build up the walls of Jerusalem.
19 Then you will delight in the sacrifices of the righteous,
in burnt offerings offered whole;
then bulls will be offered on your altar.