Bring Bach back to life—in a way, that is the goal behind Colorado Bach Ensemble, a chorale dedicated to performing the music of Johann Sebastian Bach and his compeers. Tonight, the series focuses on Ich hatte viel Bekümmernis in meinem Herzen, BWV 21 (or I had much sorrow within my heart). Artistic director James Kim will take admirers on a “guided tour” of the cantata before the group presents the full piece.