Passacaglia in D minor, BuxWV161

This is probably one of my top half dozen or so pieces by Buxtehude. I like it with a slow build to the end, but it's often (usually?) kept quite gentle throughout.
There's a theory is that there's a numerological connection to the moon. The bass theme is iterated 28 times in four lots of seven (four lunar weeks making up a lunar month), with short connecting passages to modulate to the new key. Firstly in D minor, then in F major, followed by a minor and finishing up in D minor again.