The last time the CSO performed Bach’s Magnificat was in June 1968, and the time before that was in 1930. It’s hard to see why, because this is a wonderfully moving, architecturally balanced masterwork: it begins and ends with the same joyful music, and the opening text is “My soul doth magnify the Lord,” the closing “As it was in the beginning.” It has 12 short movements that often display Bach’s soulful, melancholic side, as in the wistful aria for soprano “Quia Repexit,” which is really a duet for soprano and oboe, and the trio for two sopranos and contralto “Susceptit Israel” is gorgeous. Also on the program is Mozart’s deeply stirring, often sublime Requiem. Yes, there’ve been other local performances of this glorious work this year in celebration of the composer’s 250th birthday, but the CSO and its chorus will probably top them all. The soloists will be soprano Marlis Peterson, mezzo Anne-Carolyn Schluter, contralto Ingeborg Danz, tenor Thomas Michael Allen, and bass Nathan Berg. Mozart of course died while writing the Requiem, and other people finished it–the topic of the “Beyond the Score” lecture by Mozart scholar Robert Levin and conductor Helmuth Rilling that opens the 3 PM program on Sunday, May 21, to be followed by a complete performance of the Requiem. Both works will also be performed at 1:30 PM on Friday, May 19, and at 8 PM on Saturday, May 20. Thu 5/18, 8 PM, Orchestra Hall, Symphony Center, 220 S. Michigan, 312-294-3000 or 800-223-7114, $19-$120.