I travel back from London with the St Matthew Passion filling my head, after the moving performance from the Elysian Singers and Royal Orchestral Society under Sam Laughton at St James’s Piccadilly. Why does that last chord send shivers down the spine? The dark instrumentation, the sense that it is not an ending but a beginning, that this shadow-filled saraband will repeat itself for ever? Or is it just the story — surely one of the greatest narratives in all literature, in which nothing is redundant and yet everything is said? I arrive home with the chord still in my...