Psalm 51

Kings in that world did not publish their failures. Assyrian and Egyptian royal inscriptions record victories, building projects, and the favour of the gods; a monarch's private disgrace never went into the archive. Israel put its king's confession into the national songbook and had the choir learn it.

Hyssop was a small bushy plant used as a brush. The Law calls for it twice: to sprinkle blood on a cleansed leper, and to sprinkle the water of purification on anyone who had touched a dead body. When David asks to be purged with hyssop he is asking to be handled like a leper or a man fresh from a corpse — the two conditions that shut a person out of the camp.

There was also a legal wall in front of him. The sacrificial system covered sins of weakness and error. For deliberate adultery and deliberate murder the Law prescribed no offering at all; both carried a death sentence, and Numbers says plainly that no ransom may be taken for a murderer. That is why the psalm says God does not want a sacrifice — not because offerings were worthless, but because in this case there was nothing on the price list to bring. All he had left to hand over was himself.

The last two verses pray for the walls of Jerusalem to be built. Many readers take those lines as a later addition made when the walls were down; the traditional reading is that the king whose sin endangered the city he had just made his capital prays for the place he put at risk. Either way the temple kept them, because a congregation singing this needed a way to pray for the whole city and not only for one man.