The majority of Mozart's Salzburg Masses were written at a time of social and aesthetic change - changes that also affected sacred music and, above all, the role of music in celebrating Mass. In the years around the middle of the 18th century, settings of the missa solemnis were notable for their lavish instrumentation and for their interplay between elaborate fugal writing for the chorus and virtuoso, aria-like passages for the vocal soloists, their individual sections often so distended that churchgoers may well have thought that they were attending a concert rather than a service. But by the final third of the 18th century a countermovement had come into existence, initially within the church itself, that aimed to introduce a simpler fornt of sacred music and that finally received support from the reforms of the Emperor Joseph II. It was in the wake of this development that a more modest, shorter form of the Mass, the missa brevis, came to prominence. As Mozart told his teacher, Giovanni Battista Martini, in a critically worded letter of 4 September 1776, the Prince-Archbishop of Salzburg, Hieronymus Colloredo, now insisted that “a Mass, with the whole Kyrie, Gloria, Credo, Epistle sonata, Offertory or motet, Sanctus and Agnus Dei must last no longer than three-quarters of an honr".
It is interesting to observe the way in which the two leading composers of the period dealt with these rcstrictions: Joseph Haydn simply stopped writing church music during these years, returning to the medium of the missa solemnis only towards the end of his life with his famous six late Masses, while Mozart, by contrast, made the shorter missa brevis very much his own, turning it into a vehicle for his highly personal religious views.

Mozart's Salzburg Masses have often been described as purely functional, but it must be remembered that at this time every piece music was intended to serve some function or other. Although he did not ignore existing conventions altogether, Mozart was still able to fill out the prescribed form of the Mass with his own very personal ideas. None of these settings could be described as mere hackwork, but all are the expression, rather; of a very personal approach to religion. Several contain a  serenely cheerful, even childishly naïve view of paradise, while the many elements of folk music and even dance that are found here produce an impression of gaiety that on occasion extends to boisterous joviality.
Mozart developed his own specific musical imagery for thw individual sections of the Mass. In the Kyrie, for example, he very often creates an impression of majestic unapproachability, while the Christe tends, rather, to emphasise the human element. And in the gestures of entreaty at the words "eleison" and "miserere" and also in the "Dona nobis pacem", we often find writing that is urgent and impatient and even angry in its demands. In the "Qui tollis", the sheer weight of the burden of sin can he physically felt in the instrumental accompaniment, and at the words “judlcare vivos et mortuos", the Last Judgement is generally depicted in a way that implies great rigour but occasionally also a certain childlike naïveté. In the "Crucifixus" we can sometimes hear the blows with which the nails are driven into the Cross, whereas the passages associated with the words "Spiritus Sanctus" are always rery light in tone, dancelike and almost ethereal, like a bird on the wing. The Sanctus expresses a tremendous sense of awe and the Benedictus, finally, occasionally suggests the triumphant entry into Jerusalem, while on other occasions assuming the form of gentle music for the Elevation, its paradisal lightness of touch evoking the idea of Christ's presence in the Eucharist.

The Missa in honorem Sanctissimae Trinitatis in C major K. 167 presumably received its first performance on Trinity Sunday - 6 June - 1773. Forrnally speaking, it represents a hybrid form of the Mass, combining elements of the missa solemnis and missa brevis. Its lavish orchestral resources, including four trumpets (two of which are scored for the clarino register), timpani, two oboes, two violins, bass and organ, together with its extended instrumental preludes and interludes, the concluding fugues in the Gloria and Credo and the fugal "Dona nobis pacem" all reflect thc tradition of the missa solemnis, yet Mozart also sought to meet the then current demands of the missa brevis type of Mass with the succinctness of his setting and the relative lack of textual repeats. Particularly striking is his decision to dispense with any vocal soloists: the work is scored throughout for chorus and orchestra, with the highly contrastive and emotionally charged instrumental writing often claiming attention over the generally homophonic choral textures. Especially effective is the contrast between the mysterious-sounding a cappella passages in the "Et incarnatus” and the abrupt transition to the "Crucifixus", which is shot through with interjections on the strings suggesting voices raised in outcry and illustrating the drama of events as they unfold on Golgotha.

K 258 is a typical missa brevis, albeit one of a festive nature, its character determined, above all, by its lavish orchestration, with two trumpets, timpani, three colla parte trombones and two oboes (the parts for which were discovered only later), in addition to the usual strings, bass and organ. It is unclear whether the work was written to mark the ordination of the Salzburg canon, Count Ignaz Joseph Spaur, as assistant bishop of Brixen, since this last-named ceremony took place in November 1776, whereas the work itself is dated December. The independent orchestral writing, often drawing on motifs from folk music and dance, is contrasted with the spare but emotionally charged writing for chorus and soloists. With its interplay between majestic choral passages and more lyrical solo episodes, the lively, triple-time Kyrie is reminiscent in character of a rondeau. There are very few textual repeats in the Gloria and Credo, where the contrast between the lyrical tenor solo of the "Et incarnatus" and the darkly threatening choral cries in the "Crucifixus", underscored by the oppressive sonorities of the three trombones, is particularly affecting. The very brief Sanctus is followed by an animated, dancelike Benedictus, its interplay between solo quartet and choral outbursts illustrating the idea of a festive procession. A serenely lyrical Agnus Dei brings the work to an end.

Like K. 258, K. 259 is also believed to date from the end of 1776 and may have been written for the Feast of the Innocents, 28 December, which was also the day reserved for the members of the boys’  choir who sang the soprano and alto parts in the  Salzburg Cathedral choir. The work fully reflects Colloredo's demand for brevity, a demand ironically encapsulated in Mozart's comment that "a special study is required for this type of composition". Two trumpets, timpani and (in some of the copies of the parts) oboes lend this missa brevis its festive stamp. It takes its name from the concertante role of the organ in the Benedictus.
The Kyrie is almost folklike in its ebullient mood, while the extreme brevity of the Gloria is further underlined by the rapid interchange between solo and choral sections. At the heart of the ternary Credo is the liltingly lyrical “Et incarnatus" for solo quartet followed by the emotionally intense "Crucifixus" for choir. Mozart wrote two versions of the Sanctus, later deciding in favour of the second one. A particular high point is the Agnus Dei, which anticipates the cantilena of the Countess's aria, "Porgi, amor", from Act Two of Le nozze di Figaro. Overall, K. 259 contains clear structural parallels with the Missa brevis K. 247. But perhaps the particular charm of this setting lies in its natural simplicity, a simplicity that exudes a cheerful and folklike piety.
The present recording is supplemented by two brief sacred pieces. Cast in the form of a canon for five soprano voices, the Kyrie in G major K. 89 (73k) was probably written in 1772 in the context of Mozart’s lessons in counterpoint with the famous Bolognese pedagogue, Giovanni Battista Martini, who was one of the leading teachers of imitative counterpoint, an art that formed an essential part of the sacred music tradition of the 17th and 18th centuries.
The Offertory, Misericordias Domini, in D minor K. 222 was written in Munich in early 1775, when Mozart was in the city for the first performance of his opera La finta giardiniera on 13 January. With its elaborate contrapuntal writing, this piece provides yet further proof of Mozart's mastery in this particular form. In writing it, he was picking up an older Salzburg tradition and partly reworking material from a piece by Johann Ernst Eberlin.