Inspired by a Company engagement at the Edinburgh Festival and set to an evocative Mendelssohn score, Balanchine’s Scotch Symphony, for a lead couple and a corps de ballet, is a nod to the romantic tradition of ballet. Jerome Robbins’ enthralling Glass Pieces, a perennial favorite in the repertory, moves through moods to rise to a galvanizingly energetic finale. And while Justin Peck is celebrated for his high-energy ensemble works, Belles-Lettres reveals another aspect of his voice, with its series of gently lyrical pas de deux and solos steeped in an air of reflective romanticism.