All symphonies were sacred symphonies, once. Haydn began each day’s composition with a prayer, and ended every score with the words ‘Laus Deo’. ‘These thoughts cheered me up,’ he told his biographer Albert Dies. Haydn, like Mozart, was a lifelong Catholic, and the Swiss theologian Hans Küng has suggested that the daring, exuberance and glorious wholeness that characterises even Mozart’s secular music comes from a specifically Catholic understanding of the universe: of salvation perceived not as an object of struggle, but as an unshakable, all-embracing certainty.