Mozart may well have composed fifteen masses, several vespers, litanies and a good number of motets during his Salzburg years, but didn't consider church music as his primary concern. As soon as the musician left for Vienna, he invested all his energy in composing symphonies and concertos, chamber music and of course opera. In January 1783, however, Mozart told his father that "the score of a half-composed mass was awaiting completion". He had seemingly vowed to compose another mass if his wife's first delivery went well. Later that same year, the composer visited Salzburg for the first time with his wife Constanze. At that point, the composer still hadn't finished his Mass in C minor, which was lacking the end of the Credo and the whole of the Agnus Dei. The unfinished work was nevertheless performed on 26 October 1783 in St Peter's Church, the gaps probably being filled in with pieces borrowed from Mozart's previous masses. The composer let his wife sing the soprano solo parts, which have a very operatic allure in the Christe eleison, Laudamus te and Et incarnatus est sections. Mozart shared in this Mass his new understanding of baroque music, which he had learned through the works Baron van Swieten had introduced him to in Vienna. The Cum Sancto Spirito and Hosanna sections, in particular, show off some very masterly fugues. After the Salzburg premiere, Mozart never attempted to complete his Mass in C minor and hardly ever returned to church music until his final composition, the Requiem in D minor (which also remained unfinished). He did, however, use once again the music of the Kyrie and the Gloria. He set these two parts to an Italian text and added two newly composed arias to produce the cantata Davidde penitente which had been commissioned by the Vienna Society of Musicians.