Have mercy on me, O God, according to your steadfast love; according to your abundant mercy blot out my transgressions. -Psalm 51:1

Psalm 51 teaches two things: mercy and sin. But aren’t we already experts in sin? Why do we need God to teach it to us? Well, we are good at pointing the finger to say, “There is a sinner!” But it takes hard schooling to say, “I am a sinner—indeed nothing but sin (‘in sin my mother conceived me’ (v. 5) and ‘I only sin before you’ (v. 4).” But what about my good created nature, my free will, my possibility for change? No. David is not a medieval scholastic or American evangelical. Thus, he learned all theology in one fell swoop: I, the sinner! God the justifier! There is nothing more you need to know.

Yet, the only thing that takes more schooling than my own sin is God’s justification—because it is illegal. David already knew he was a scoundrel, as most kings are, but he didn’t know that his real sin before God was his best quality—enthusiasm (trying to make God’s word true, faster). David learned that sin is a matter of law and gospel, not law alone. So if you get your own sin wrong, you get grace wrong too. The old seminary teachers defined sin as anything said, done, or thought against the Law of God. Simple. That, in turn, made church repentance into a process of:

1. Thinking back over the past year.

2. Naming the specific sins.

3. Having sorrow over them.

4. Expiating them by “satisfaction” for the infraction.

This process tells me that my main concern as a Christian is to train my will's desires to want higher, spiritual things rather than lower, bodily things. Luther’s teachers figured the will was good in essence (God doesn’t make junk), but through malice, the will is misled, so a person may at best be able to keep the law in the act but always falls short of having the right intention. Thus, churches were there to improve our intentions. This is like telling a servant she isn't setting the table properly because she isn’t dressed all in white while doing it—as if God requires the ten commandments … and then something more!

Instead, David actually started with the simplest commandment (coveting) and suddenly discovered he had broken the whole shebang: adultery, murder, false witness, stealing, dishonoring parents, dragging Israelites into war, and finally leading the enemies of Israel (the Ammonites) to blaspheme the first commandment because they conquered Israel so easily and took God to be “no god!” From one sin we learn them all. But then David found himself bereft of the one thing he needed: a preacher.

Nathan was sent by the Spirit to David (2 Samuel 12) and told David the tale of a man with “one ewe lamb,” who treated it “like a daughter to him”—which was better than David ever treated God’s promise. So Nathan caught David in the act. Of what? Not just pornography but denying the promiser—since the promise to David was directly attached to David’s activity in bed. David’s seed had a promise in it, and where he put it mattered to God.

Suddenly the true confession came out. David said to Nathan, “I have sinned against the Lord.” But Nathan’s job was not done. The next day the preacher came with: “Now the Lord has put away your sin; you shall not die.” Then what? “Nevertheless, because by this deed you have utterly scorned the Lord the child that is born to you shall die.” Yet, this was not God’s need for satisfaction by law (a pound of flesh) but God refusing to let enthusiasts mess with his promise. God insists that the Seed be Christ. He chooses what Seed rules forever, when, and where—not David. He even let Bathsheba house the promise, since David himself was only the instrument. David must wait for Christ, not make his own Christ.

David’s psalm begins, so full of the faith’s surprising words that we cannot contain them all: “Have mercy on me, O God, according to your steadfast love; according to your abundant mercy blot out my transgressions” (Psalm 51:1). Faith always has these three sentences:

1. Have mercy!

2. On me!

3. O God!

How does David figure God will give this mercy to me? Not in my mind or in my will—but in my ear by hearing a sermon. And how will there be a sermon, unless there is a preacher? And how will there be a preacher, unless one is sent? And who will send one if not the Holy Spirit? O, how beautiful are the feet of those who come over the mountain!

David’s sin was that he had no preacher. What to do? God sent a preacher who blotted out David’s transgression so that if David ever went back to ask what happened to this sin concerning Bathsheba, Uriah, and the hidden God of majesty, the preached God would say: What sin?s