Bach's Fuga sopra il Magnificat BWV 733 - It's not a good idea to compose a Fugue about songlines so simple that you can't call it a melody: if you try, you're not likely to get very far. Yet, this is the case with the Magnificat - a few simple lines of notes to help the priest along with the Canticle of Mary. The early medieval form had firmly established its place in the Liturgy of the Mass and Vespers. The translation into 'Meine Seele erhebt den Herren" (My soul magnifies the Lord) is likely from Martin Luther, but the original Gregorian chant survived the Reformation. Perhaps because it was using the noni toni or tonus pregrinus (D Dorian), where "pregrinus" connects to "pilgrim", "traveller" or "foreigner" (The Luke 1 story: Mary travelled some 120kms to visit Elizabeth where she sang her song), or because "Visitatio Mariae" was firmly on the Lutheran liturgical calendar, history shows that Bach kept using the Canticle lines in BWV 733 as well as his Cantata "Meine Seele erhebt den Herren" (BWV 10).
The Dutch Bach Society concludes: "Bach fools his listener with a quasi-fugue" (1), while tonus pregrinus expert Mattias Lundberg calls the melody a "quasi-chorale" (2). Nevertheless, the young Bach succeeds in crafting a coherent composition, where all I hear is no less than six minutes of persistently maintained glorification of the heavens: rolling waves of overtones and jubilant themes captivating any cathedral's reverberation, hypnotising the listener and expressing exactly what is intended: a seemingly never-ending waterfall of heavenly magnificence.
In recent years suggestions have surfaced about possible authorship by Johann Ludwig Krebs, but evidence is not conclusive. Even though Bach, Krebs’s teacher, had enormous respect for his student, referring to him as "the biggest crab (Krebs) in the brook (Bach)," for me BWV 733 remains a Bach composition.