Many Renaissance theologians, such as Ficino, related the Mosaic seven-day creation week as a "metaphor" for the ordered process, according to the heptachord
structure found in Plato's Lambda Formula (Rostvig, Configurations 17).
Seven heavenly spheres form a heavenly heptachord
, whose every planet corresponds to a certain string of a kithara, i.e., the cosmos is imagined as a huge musical instrument (Boethius 1867: 188-189).
Also known as the heptachord
, the seven-string lyre appears on many ancient Greek vases in the hands of Orpheus.
Bach's wish to complete the series of letter-names (which perhaps replaced an earlier intention to cover a simple heptachord
, continuing the 'scissors' movement outwards to F and then stopping) must be the reason for the transposition of the overture from its original key of C minor.
For example, 6-Z3  is (abstractly) covered by/embedded in six different heptachord