The status of church music within Mozart's overall output continues to be hotly debated. This is especially true of the composer's early Masses, which are also among his least-known works. The pieces recorded here all date from the period between 1768 and 1775 and all attest to the adolescent composer's impressive artistic achievements within the simple confines of the missa brevis or "short mass". All the different wavs of setting the Ordinary of the Mass that were then current in Southern Germany and Austria - the missa brevis for non-ceremonial Sunday services, the missa solemnis for cerernonial High Masses anrl the hybrid form of missa brevis and missa solemnis (a type notable for its use of trumpets and timpani) - were thoroughly familiar to Mozart. "My father is conductor at the Cathedral, so I can write as much church music as I want,” the selt-assured composer informed Padre Martini in Bologna in September 1776.
Two factors are crucial to Nikolaus Harnoncourt`s approach to these Masses: the undisputed mastery of the youthful composer's first essays in the genre and the love of life that finds expression here, a joie de vivre that threatens to outstrip even Mozart`s chraracteristic ebullience. From a presentday perspective, such high spirits may appear puzzling in the context of the liturgical function of the works in question, but the mood in Salzburg in the 1770s must have been hedonistic in the extreme, if we may trust Johann Caspar Risbeck's Letters of a French Traveller: "Everything here breathes a spirit of pleasure and enjoyment. People feast and dance, make music, love and gamble to an insane degree, and I have yet to see a place where one can enjoy so many sensual delights for so trifling an outlay." Such a claim is all the more striking when we recall that the then Archbishop, Hreronymus Colloredo, had a reputation for strictness and for upholding Enlightenment principles.
To modern listeners, Mozart's "faith" can seem baffling, and much has been written - often of a highly speculative nature - on the apparent contradiction between his lifestyle and the religious convictions expressed in his letters. Nikolaus Harnoncourt is convinced that this contradiction is a later construct based on the fact that we have lost touch with the sort of conditions that existed in the late 18th century. “I see 18th-century Catholicism as colourful and full of the joys of life, just like the churches of the time." The strict separation between earthly and celestial delights seems not to have existed at that time. Perhaps it was the certainty that, as a result of the sacrament of penance, our sins will be forgiven while we are still on earth which, in the Catholic world, made the act of praising God so markedly sensual an experience.
This sensuality found expression not only in the magnificence of Baroque architecture, with its roguish putti, but also in the sacred music of the period. Divine worship was seen not as a solemn and grimly determined act of penance designed to ensure the soul's salvation, but as a natural part of the daily round, something as necessary as eating and drinking and performed with the very same pleasure. It is no longer surprising that, seen in this light, many of Mozart's Masses are so exuberantly joyful in character.
“You have to take their religious content entirely seriously." says Nikolaus Harnoncourt. “It is extremely profound and heartfelt music. But just as important is the humour, the lightness of touch, the life-affirming element. In my mind's eye I see florid-faced clerics bursting with life, and mischievous servers who don't pay proper attention but always come in a bar too soon and receive a cuff round the ears for their pains. And there is invariably the twittering of birds to represent the Holy Ghost." 
The striking violin figures in the Allegros from the Sanctus and Benedietus of the Missa brevis K 220, to which the whole piece owes its nickname of Spatzenmesse or “Sparrow Mass", certainly come under this heading. This relatively popular work marks the first high point in Mozart's career as a composer not only in terms of the rigour of its compositional structure (a rigour achieved by means of the motivic link between its beginning and its ending) but also in respect of the economy of its instrumentation, with its simple church trio (first and second violins plus bass) supplemented by trombones, natural trumpets and timpam. The result is a missa brevis et solemnis.
Mozart clearly regarded these external constraints not as a restriction but as a challenge. In the letter to Padre Martini from which we have already quoted, he reports that in Salzburg "even the most Solemn Mass, when said by the Archbishop himself," was not allowed to last “longer than three quarters of an hour. So you see that a special study is required for this kind of composition, since a Mass like this has to be scored for all the different types of instrurnents such as trumpets, timpani & c.". 
The two early Masses K. 49 and K. 65 predate Mozart's extended visits to Italy and are both astonishing pieces in terms of their elaborate contrapuntal writing and their sensitive response to the text. What is most remarkable, however, is the fact that the twelve-year-old composer does not merely juxtapose the separate sections of the Ordinary of the Mass but combines them together to form a coherent whole, imposing upon them a sense of structure that was to leave its mark on the much older Michael Haydn, who openly admitted that he had been decisively influenced by Mozart's sacred music. Mozart’s earlv mastery of this medium is also clear from his Missa brevis K. 194 of 1774 and, in particular, from the freedom of his handling of its vocal textures.
For Nikolaus Harnoncourt, there is a further aspect of Mozart's Masses that is of decisive importance. "These works are veny much bound up with folk music - in a very subtle way this has to be brought out in the manner in which thry are performed."
The Vienna Concentus Musicus, whose strings and winds are thoroughly at home in the Austrian performing tradition, are able to communicate this idiom with quite unmistakable charm.