Johann Sebastian Bach is one of the most famously unfathomable composers in the history of music. How can such sublime work have been produced by a man who (when we can discern his personality at all) seems so ordinary, so opaque - and occasionally so intemperate? It is rare that such an accomplished performer of music should also be a such considerable writer and thinker about it. John Eliot Gardiner takes us as deeply into Bach's works and mind as perhaps words can.