Psalm 51 is one of the so-called ‘Penitential Psalms’, the fourth in fact. It begins:
Have mercy on me, O God, according to your steadfast love; according to your abundant mercy blot out my transgressions. Wash me thoroughly from my iniquity, and cleanse me from my sin.
It goes on in this tone until a glimmer of light in verse 12 (the last of the selection for this week).
Restore to me the joy of your salvation, and sustain in me a willing spirit
The situation is given an even sharper edge by the preceding OT reading from Samuel after Uriah was killed. How would you like to be in Nathan’s shoes? Just pop in to King David plucking his lyre in the grand throne room and tell him straight that he really blew it: time to really face the music.
Result: penitence — and Nathan kept his head.
Music
As we noted in the previous Crystal Ball post, there are dozens of settings available, some of them quite grand. I have written on these settings in earlier posts. We hear the psalm as a reading this week rather than in song.
Singers assemble in force again for Sunday 9th, rehearsal Saturday 8th from 4pm, for no less than six very different short musical selections for mixed and male voice groups.
Reprise — previous posts on Psalm 51:
Psalms in the South 
Thanks Brendan