1st Part (0:00-0.57) is an Fragment by D. Buxtehude (BuxWv 154)
2nd Part is a reflection of the Fragment (tonality, lyrian with 5+)
3rd Part is an Passacaglia
4th Part: the Theme by Buxtehude is knocking (Carrillon)
5th Part: Amen-Toccata about "Auf meinen lieben Gott" (Ped c.f.)