Bach became the Weimar court organist in July 1708, and one of his most striking and renowned pieces, the Passacaglia and Fugue in C minor, BWV 582, was probably composed at about that time. Bach took four bars from a much smaller passacaglia by the French organist André Raison and expanded it to eight measures. (The theme is also similar to ones used by Dieterich Buxtehude, and Bach’s piece may have been an homage to the older composer, who died in 1707.) After stating this theme starkly alone in the pedals to begin, Bach builds 20 variations over, under, and around it. The theme then explodes into a massive double fugue of astonishing virtuosity for both creator and performer.

There has been much research and even more speculation about the possible organization and subdivision of the variations, yielding numerological relationships to subjects ranging from Buxtehude to the Lord’s Prayer. At its simplest, the 21 variations (counting the original statement in the pedals) become 3 X 7, numbers highly fraught with symbolism. This can have an impact on interpretive decisions, particularly registration (choice of stops), but Bach gave the work tremendous color simply through changes of range and texture. He also uses rhythm with tremendous verve as a structural and directional element, from the almost proto-Brahmsian syncopation of the first variation through the relentless drive of the fugue.