From 1772 onward, Mozart wrote 17 short single movement works called Epistle Sonatas, designed to be played in the Eucharist service between the Epistle and the Gospel. The Epistle Sonata in C (K.336) was the last of these, written in 1780. Shortly afterwards the Archbishop decreed that a motet or hymn should be sung instead, and they fell into disuse.
The Epistle Sonata in C was originally scored for two Violins, Basso Continuo, and Baroque Organ. It has been arranged for solo Organ (with pedals) by Nigel Davison.