Here’s a brief overview of the first movement of Mozart’s Great Mass in C Minor.
When we sing a Mass by Bach, or Haydn, or Mozart, we are singing a setting of what is called the Ordinary of the Roman Catholic Mass service. The Ordinary has five movements: the Kyrie, the Gloria, the Credo, the Sanctus, and the Agnus Dei. Each movement is divided into several sections, based on the text.
The Kyrie has a tripartite structure (“Kyrie eleison, Christe eleison, Kyrie eleison”). The first Kyrie opens with a dramatic arpeggiated melodic gesture in all the voices, then moves into a texture contrasting long phrases with groups of 16th notes and staccato 8ths.
In the Christe eleison, a section almost assuredly composed for Mozart’s wife Constanze, this is a complete contrast to the enclosing Kyries: it is warm and lyrical and also operatic in character. The chorus responds to the soloist’s four-bar phrases, the music builds to a forte statement of “eleison” and then the soprano takes off on her own, singing in a range spanning two octaves. The music starts over with the dolce rising “eleisons” (m. 58), then becomes highly decorative as the soprano leads us into the return of the Kyrie theme.
Usually the music of the first Kyrie repeats at the statement of the second Kyrie. Mozart does this but makes an interesting artistic decision. True to the conventions of the sonata allegro form of his time, he writes the contrasting Christe eleison section not in c minor, but in the relative major of E-flat. Then, returning to the Kyrie text, he skips the first phrase (the rising melodic arpeggios sung by each vocal section) and begins his recapitulation in E-flat with the second phrase – the long, soaring soprano line:
A couple of things: notice how in the second Kyrie the tenors sing the exact same notes as the altos did in the first Kyrie (mm.13-14) while moving us back into c minor. And listen for the beautiful deceptive cadence at measure 91: the G7 chord moves to A-flat instead of to C – this signals the end of the movement coming. After four gorgeous, breathless chords, the singers cadence on C minor and the violas reiterate the violin melody from the beginning of the piece. Such a pleasure to sing this beautifully-constructed movement.