Clavier-Übung means "Keyboard Practice." Bach wrote four cycles by that name: Vol. 1 the six partitas for keyboard, Vol. II the French and Italian Suites, Vol. IV the Goldberg Variations, and Vol. III--written for the grandest instrument of the keyboard family--the so-called "Organ Mass." Volume III is called the "organ mass" because it consists of a series of chorale preludes on texts pertaining to the Lutheran Mass and Catechism.
Framing Prelude and Fugue
The Clavier-Übung III begins with a prelude on the hymn Was mein Gott will, das and concludes, twenty-seven movements later, with a triple fugue using that hymn tune as the basis for its three subjects. Because the German chorale is similar to William Croft's "O God Our Help in Ages Past," English organists began calling these the "St. Anne" Prelude and Fugue. Separation of the "St. Anne" fugue from its prelude indicates that Bach intended this melody to frame the intervening chorale preludes as follows:
Symbolic of the Holy Trinity
The many incidences of three's in the prelude and fugue--3 flats in the signature, 3x3 sections in the prelude, 3 subjects in the fugue in 3 proportional meters--are intended to invoke the name of the Holy Trinity. This symbolism continues in the twenty-one intervening chorale preludes and four duets which have three functions in the Lutheran liturgy: the Mass, Catechism and Communion.
Nine Preludes on the Mass Ordinary
The first nine chorale preludes employ texts related to the German Mass ordinary: Kyrie and Gloria.
Twelve Preludes on Luther's Catechism
The second group of preludes employs twelve settings of six texts elucidating the six parts of Luther's Short and Long Catechisms. Each text is set twice: once for full organ and once for manuals only. The six parts of Luther's Catechisms are as follows with corresponding melodies of Bach's Clavier-Übung III in italics:
The Ten Commandments: Dies sind die heilgen zehn Gebot
The Creed: Wir glauben all an einen Gott
The "Our Father": Vater unser im Himmelreich
Baptism: Christ, unser Herr, zum Jordan kam
Penitence: Aus tiefer Not schrei ich zu dir
The Eucharist: Jesus Christus, unser Heiland
Bach uses the musical devices of canon, melody in pedal, and full organ, to reinforce Luther's theological organization in the following manner. Sections 1 & 3 interlock as they quote from Biblical canon: the ten commandments of the Old Testament and the "Our Father" of the New. Bach uses canon to reinforce Luther's pairing of these two sections. Similarly, Bach sets the melody in pedal to reinforce Luther's pairing of sections 4 & 6: the sacraments of Baptism and the Lord's Supper. Finally, in sections 2 & 5, Bach uses full organ to reinforce Luther's confessions of faith: the Creed "I believe in God" and Penitence "I will hope in God."
Four Communion Duets
The final group are duets intended for use during communion. Because Luther prefaced his Catechisms with four application precepts, some writers have suggested that these duets represent the appropriation of doctrine (catechism) in the Eucharist. In his "Esoteric Structure of Bach's Clavier-Übung III" (Cardiff: University of Cardiff Press, 1983), David Humphreys theorizes that modal relationships in the duets appeal to the classical Greek symbols of pedagogy as follows:
Canon as Image-Evoking Structure
As mentioned earlier, the two canons of the Clavier-Übung III exist to reinforce the theological outline of Luther's Catechisms. Such use of a musical technique to make a theological point reveals Bach's conception of canon as expressive of spiritual realities transcending technique or sound. The two texts set in canon--the Ten Commandments and the "Our Father"--come from the Old, and New, "Canons" respectively.
But Bach's use of canon does more than reinforce the symmetrical structure of Luther's Catechisms. In the Ten Commandments, canon functions as a text-generated figuration reminding Israel to "teach them diligently to your children," reciting them literally "when you sit, walk, lie down, and rise up" (Deut. 6:7). In the "Our Father," canon can be seen as a figuration of Jesus commandment "in this manner you should pray" (Matt. 6:9). Of the many image-evoking structures in Bach's music these canonic preludes are evidence that the composer thought deeply about his texts. The musical idea was not imposed upon them but quite the opposite.
The Two Canons of Clavier-Übung III
The canons of the Clavier-Übung III are chorale preludes in which the chorale melody comprises the seed. Both canons at the octave, the cantus firmus for each chorale prelude follows:
In Dies sind die heilgen zehn Gebot Bach times the entry of the canon follower so that the six repeating pitches of the cantus firmus are extended to ten (10 commandments).
In Vater unser im Himmelreich Bach weaves a tapestry of independent voices employing more than 250 reverse-dotted rhythms in the Lombardic style. Bach normally restricts Lombard rhythm to his vocal music and nearly always with extra-musical intentions. Here Lombard rhythm portrays the majesty of God in his Himmelreich.