In 1773 Mozart was staying in Milan to play his opera titled "Lucio Silla" in which used a male soprano singer (of the type called castrato, frequently used in operas and oratorios during the baroque period.) Thia piece is a motet for the male soprano.
A motet is a vocal form with lyrics which originated and developed in Medieval Europe, as both secular and clerical music.
Although Mozart uses religious verses in Latin for this motet, the whole inpression is that of operatic glamour, and its 3 - movement composition in quick-slow-quick tempo reminds us of a vocal baroque concert.
