During Holocaust, why did Jews sing Verdi’s Requiem to their captors?

Located 30 miles north of Prague, Terezin/Theresienstadt was turned into a Jewish ghetto and concentration camp by the Nazis after their occupation of Czechoslovakia. The camp was unusual in that inmates included highly educated Jewish scholars and scientists as well as internationally renowned artists, musicians and actors including Czech composer Rafael Schächter and the famous German rabbi Leo Baeck.