Above all, it summarizes the entire known potential of counterpoint.
Etymology is well and good.
But the form is understood only when its principles are fully realised as they are within this masterpiece. No one understood the workings of counterpoint more fully than Bach and in his final years the composer, then Cantor at St Thomas's, Leipzig, was more and more preoccupied with contrapuntal music. It proved a monumental revelation, an unfinished series of contrapuntal variations imbued with unfailing variety and limitless imagination. But his overriding aim was purely to exhibit the comprehensive possibilities of a single, simple 'subject' with various types of fugal and canonic writing. Bach's debilitating final disease prevented its completion.