Bonaventure

Just as God completed the whole world in six days and rested on the seventh, so the lesser world may be led in most orderly fashion through six stages of successive illuminations to the repose of contemplation. As a figure of this, one ascended by six steps to the throne of Solomon; the Seraphim that Isaiah saw had six wings; after six days the Lord called Moses from the midst of the cloud, and Christ after six days, as is said in Matthew, led the disciples up the mountain and was transfigured before them.

Itinerarium Mentis in Deum, Chapter 1 ↗