In 1957, Margaret Hillis was asked by Chicago Symphony maestro Fritz Reiner to form a resident symphony chorus. Today, many memorable concerts and seven Grammys later, the Chicago Symphony Chorus is commonly acknowledged as the best of its kind in the world. Along the way, Hillis has tirelessly championed the cause of choral music, encouraged the formation of choral organizations both within and outside Chicago, and helped launch a number of important singing careers. Her dedication to her metier, as her choristers will tell you, is total. This concert, ostensibly a commemoration of the chorus’s 30th anniversary, is really a tribute to Hillis’s lifetime achievement and an affirmation of her conducting skills. You can expect the performance of Masada (1972), a large-scale, old-fashioned oratorio by Marvin David Levy based on the ancient Hebrew tale of courage and fortitude, to be seamless and superb. As always, Hillis won’t settle for anything less. The solo tenor in this world premiere is Gary Bachlund; the narrator is Yael Dayan (daughter of Moshe). Thursday through next Saturday, October 17, 8 PM, Orchestra Hall, 220 S. Michigan: 435-8111.