This piece consists of a “Voorzang” (the melody of a psalm presented by a singer) and a Trio on the same melody. In this case the melody of the 75th psalm (Geneva 1562).
The “Voorzang” is an anonymous piece, but set by “eene zeer kundige hand” (a very able hand) in the opinion of it's contemporaries.
Klaas Bolt (1927-1990), organist of the Grote St. Bavo Kerk in Haarlem, one of the most famous churches and organs in the Netherlands set a trio in the typical 17th century Dutch style to it.
He was a specialist in this field.
The result is well worth listening to.