There are seven steps between earth and heaven, and that's why the number seven is associated with the initiation process. If you go through all seven grades then you are initiated into the very highest level. And seven is to eight as three is to four: it is on the way to totality.
Edinger establishes seven as the penultimate initiatory number in Hellenistic cosmology, structurally analogous to three in the triad-to-quaternity movement, pointing toward but not yet achieving psychic totality.
, Transformation of the God-Image: An Elucidation of Jung's Answer to Job, 1992thesis