Ian Page and Classical Opera’s “Mozart 250” is an ambitious 30-year project to record all Mozart’s major works and many of those of his contemporaries. We’re already three years and several fine recordings into the project, so it’s easy to forget that Mozart is still only 12 years old. If you’re still marvelling at that you’re not alone. Mozart’s Grabmusik (literally “Grave Music”) may have been the product of a similar reaction from the composer’s contemporaries. Locked in a room with manuscript paper by a suspicion patron, the young boy may well have produced this precocious work.

A dialogue between a tormented soul and a consoling angel, the cantata has a stature the charming but...