Lincoln Kirstein called it a “full-length ballet without a plot,” but George Balanchine’s Jewels—which premiered in 1967 and consists of three acts: “Emeralds,” “Rubies,” and “Diamonds”—is a castle keep of Medieval imagery, Symbolist echoes, neoclassical refractions, and the story of Balanchine’s heart. If you’ve never seen it, now’s the time. —L.J.