Celebrated Maestra Marin Alsop makes her May Festival debut, leading a program showcasing composers who crafted the American musical identity. Samuel Barber’s Knoxville transports us to a lyrical dream of a Tennessee summer, while Aaron Copland’s “The Promise of Living” rings with Midwestern hope of prosperity. Also, the “uncanny radiance” (The New Yorker) of Robert Nathaniel Dett’s The Ordering of Moses returns to Music Hall—a work the Festival premiered in 1937 and later performed and recorded at Carnegie Hall.