As remarkable as the quality of the compositions themselves is the astonishing rapidity with which Mozart composed his last two great operas, “Die Zauberflöte”, K.620, and “La clemenza di Tito”, K.621: From first sketches and drafts to finished products, some 800 pages of music penned within the six-month period from April to September 1791.

Opinions of the work at the time of its première are as varied as the history of its reception. As a “coronation” opera it initially lent itself to court...