“We have long gone to holy mass together ever since our engagement, to confession and communion and I find that I have never prayed so intimately or confessed or taken communion with such devotion as w hen I am by her side. And she feels the same. So we are clearly created for each other and God, who oversees to everything, has decreed that he will not abandon us” wrote Mozart on August 17th 1782 to his father, just two weeks after he had married Constanze. He agreed to compose a mass in gratitude to his marriage, which he planned to have performed in Salzburg when he visited Leopold Mozart together with his wife. Unlike his earlier masses, Mozart planned a grand “cantata mass”, possibly for Constanze to perform. He first mentions the work in progress on January 4th 1783: “I have the morale to write it! This is why the words are running from my pen. I have made a pledge in my heart and I hope I can keep it (…) that sincerity of my resolution is proved by the score of the mass which is half complete.” Mozart began work in July 1782 and continued until May the following year and yet he never completed it. His visit to Salzburg only took place in summer and Mozart took the semi-complete score with him, but he failed to finish it there either. Thus only the Kyrie and Gloria movements were premiered in the Salzburg St Peter’s Monastary church on October 26th 1783. The Mass in C minor was to remain unfinished: besides the Kyrie and Gloria, only a Sanctus and Benedictus was finished and of the Credo only two movements (“Credo in unum Deum” “Et incarnatus”). There was no Agnus Dei.

“We have to understand the characteristics of the style of the C minor mass in the wider context with Mozart’s contemporary activities and compositions” – warned Stanley Sadie in the New Grove Lexicon. “In 1782, he became acquainted with Baron Gottfried van Swieten in whose house he regularly performed. As the ambassador of Berlin, van Swieten became a lover of late Baroque music which was virtually never heard in Vienna outside a very restricted circle of enthusiasts. These works interested Mozart who copied down several Bach fugues and it led to him composing a suite and countless fugues of his own. The C minor mass is the first large scale Mozart composition which bears the hallmarks of his acquaintance with the style of Bach and Handel. This partly explains Mozart’s growing interest in counterpoint (this can be seen in instrumental works of this period, such as the string quartet in G major, K. 387) but also the archaic mood which appears in Mozart’s compositional palette. This style is most conspicuous in the “Qui tollis” movement of the C minor mass: the dotted rhythms of the strings evoke the character of a dignified “French overture,” the bass line follows the chromatically descending ostinato characteristic of Baroque passacaglias, while the two choruses alternate, singing weighty and sorrowful chromatic solos. We can also discover the archaic in some of the solo movements: the vocal solos of the”Domine Deus” duet and the “Quonium” trio with their elevated contrapuntal technique, as well as their baroque figurations and virtually bare continuo textures all betray the influence of Bach and Handel. The expressive melodiousness of the other solo movements and their ornamentation follow the accepted Austrian church style (“Laudamus”, “Et incarnatus”), as well as the superbly crafted “Cum Sancto Spiritu” that closes the Gloria, clearly a fugue based on the Fux type model. In the Kyrie, we find all the stylistic diversity of the C minor mass present in a single movement: the vast melodic spans of the two dark toned Kyrie sections and a strict contrapuntal structure surround the peaceful mood of the E flat major “Christe” soprano aria.
“But” – as György Sólyom writes – “this just tells us at best of the origin of the sources, the style of “baroque and ecclesiastical” and “modern, operatic” – the entire movement’s “breath”, and demeanour is a single and unbroken outpouring of Mozartean, human warmth.”

In 1785, Mozart recycled the existing movements of the mass, supplemented by two arias, for his cantata commissioned by the Vienna Tonkünstler-Sozietät, Davidde penitente (K. 469).