Vesperae solennes de confessore KV 339 of 1780 is the last composition by Wolfgang Amadeus Mozart in his turbulent career of organist and composer at the Salzburg cathedral. He had taken the job just a year earlier and began with composing a true masterpiece: Mass in C major KV 317, later referred to as the Coronation Mass. Both works of music show close relationship with the Salzburg performance practice in terms of form and instrumentation.
“Our church music is quite different from what is practiced in Italy. Even if the mass contains all standard parts, even when it is designed for a most solemn occasion with the Archbishop celebrating the mass in person, the whole composition must not be longer than three quarters of an hour. It requires experience in this kind of work, especially since all instruments should be incorporated, including trumpets and timpani” – wrote Mozart. However, with this artist the more difficult task he was facing, the grander the piece he composed. The Mass, composed for the liturgy of Easter Sunday of 1779, does in fact, last less than three quarters of an hour, so it can be used as part of ceremonial liturgies: feel free to recall the liturgical context of its performance in St. Peter's Basilica in Rome under the guidance of the musical Pope John Paul II. The individual parts of the Mass are not broken down into numbers as in solemn masses, but create a compact composition. The solo parts smoothly merge into choral, only to emerge back. The whole is accompanied by delicious instrumentation of a typical Salzburgian set of strings, consisting of a “bass” group, which includes the bassoon, and two violins. Violas were not used, neither were flutes. Wind instruments – oboes, horns and three trombones – highlighted the lower parts of the choir, followed by the trumpets and timpani, as mentioned by Mozart.
It is not known why the composition received its traditional name – Coronation Mass. Mozart himself considered it his best work in this genre, and took it with him everywhere after leaving Salzburg. The piece was performed several times during the life of the composer, including, perhaps, the coronation celebration of Leopold II and Francis I (conducted by Salieri). At the beginning of the nineteenth century, the mass became the truly most popular composition at the Viennese court ceremonies.
The Mass is a true culmination of sacral works of the emperor of composers, Wolfgang Amadeus the Great. Perhaps it is his informal coronation that the common title of Mass in C major  refers to.