Sometimes it’s like this. The elevator door slides open on the first floor and the music of Tchaikovsky fills the space around. A Symphony sextet of violinists Joo Kim and Xiaoxiao Qiang, violists Beth Guterman Chu and Jonathan Chu, and cellists James Czyzewski and Si-Yan Li rehearsing Souvenir de Florence for two Symphony Where You Worship concerts this week: Messiah Lutheran Church on Grand, Thursday; Immanuel Lutheran Church in Alton, Illinois, Friday. Free Tchaikovsky with some of the best string players anywhere. And on a Monday afternoon for a moment when the elevator door slides open.