Mozart wrote this solo motet in Milan in January 1773, at sixteen, for Venanzio Rauzzini, the castrato who had created the role of Cecilio in Lucio Silla a few weeks earlier. Rauzzini sang the first performance on 17 January in the Theatine church. It is built like a small concerto — two arias framing a recitative, ending in the Alleluia that is now heard far more often than the whole. Mozart later revised the piece for a Salzburg performance, replacing the middle sections; the Milan version is the one usually sung today.