Eddy Mul Buxtehude's Passacaglia in d: liturgical music?
Het ORGEL 96 (2000), nr. 2, 12-13 [summary]

Based on sources such as Luther's explanation of the Magnificat, Werckmeister's Musicalische Paradoxal-Discourse and the Hamburg Church Ordinance of 1699, one can assume that Buxtehude's Passacaglia in d (BuxWV 161) might have served as organ prelude in a vesper service at Lübeck, preceding the Magnificat. The form of BuxWV 161, 4 times 7, can be seen as an allegorical representation of the person of Mary, who was very important to orthodox Lutherans. If so, Mary's hymn (the Magnificat) can immediately follow the Passacaglia.