The child of a fallen angel and a mortal yearns for paradise. From this gossamer premise, Robert Schumann weaves a musical tapestry of ravishing sensuality. How to classify it? “Part oratorio and part opera,” says the copywriter for the Proms, conjuring up “a choral and orchestral cycle that seems to unfold in continuous song.” Yes, that’s about right. Sir Simon Rattle’s performance with the London Symphony Orchestra is the first-ever at this encyclopedic festival. Lucy Crowe sings the Peri, the innocent with transcendental longings. —Matthew Gurewitsch