The Greeks most probably constructed their musical tetrachords in a symmetrical order in analogy with their sculpture, and showed the ear identical with the eye in its love of symmetry. With them, therefore, the Dorian mode would have a certain pre-eminence. Beginning this mode on D, without knowing the musical mystery that resides in D, they had two tetrachords with the semitones symmetrically in the middle in one mode; it was next possible for them to arrange in pairs, symmetrically, the other tetrachords.
[Scientific Basis and Build of Music, page 45]
And it is another very interesting fact that those numbers multiplied into each other always make 720, the number in the minor genesis which corresponds to 1 in the major; F1 being the generative root of the major, and B720 the generative top of the minor; so adjusted they place the two D's beside each other - D26 2/3 and D27 - and we see the comma of difference between these two numbers which are distinctive of the major and the minor; 26 2/3 x 3 = 80, and 27 x 3 = 81, and 80:81 is the ratio of the comma. This is the Ray and the Rah in which there lurks one of music's mysteries. Let him that is wise unravel it. It is symbolic of something in the spiritual realm of things; its full meaning is only found there. [Scientific Basis and Build of Music, page 88]
See Also
great mystery of all of the mysteries of matter
music
Mysteries
Mysterium Magnum
mystery
Part 14 - Keelys Mysterious Thirds Sixths and Ninths
Wisdom in Mystery - Keelys Progress - Part 1