Erbarm dich, O Herr Gott - J.S.Bach BWV 721

1. Be merciful to me, O Lord God;
according to your great mercy
wash me cleanly of my misdoing;
I know my sin and it grieves me.
Only against you have I sinned,
and it is constantly before me;
evil cannot stand before you,
you are just, however you are judged.

Psalm 51 translated by the reformist Erhart Hegenwalt and published with the melody in Wittenburg as a broadside,1524.
This austere setting stands alone in the organ works of J.S. Bach. There are other uses of repeated chords but these are usually partnered by longer bass notes or another part providing contrast. Peter Williams refers to a cantata setting by Busbetzky, a pupil of Buxtehude, where repeated string chords accompany the chorale melody. The use of repeated quavers in the bass part of ‘Ich ruf du zir’ BWV 639 is an example of a similar pulsing breath-like pattern. The strong/weak pattern for each pair of notes or chords in the case of BWV 721, resembles an Italian string technique and an interpretation that is available to most instruments. On the organ, this ‘sobbing’ is achieved by playing the first of each pair longer than the second.
I am reminded of the repeated string chords in ‘The Cold Song’ from Purcell’s ‘King Arthur’ or Vivaldi’s writing in ‘Winter’ from ‘The Four Seasons’. Although accompanied by continuo, the style would be well known by Bach. See Henry Purcell: Cold song for Organ Duo (youtube.com)
In my recording, I have made a start at an interpretation that moves away from the slower performances normally associated with this piece and tried to imagine a baroque string style which provides tension and a sense of the need for forgiveness found in Psalm 51. I have used a pedal 4ft stop to play the chorale melody. On the Blackburn organ I have used the Swell 16’ Bourdon (played up an octave) and the Pedal Recorder 4’ coupled to the Positive 4’ Koppelflüte, providing some undulation.