Trying to clarify the relationship between the beings of the second hierarchy, spirits of wisdom, movement, and form, working from the "inside" generating physical warm/fire, and reflecting there work into the cosmos, and the beings of the first hierarchy, observing actively from the outside, with spiritual-soul warm/fire. The body of the Archai, the "egg-forms", are set in motion through the play of these two streams of will.
Old Saturn is the source of our Architectural imagination, it is where the lows of the Physical (body) were developed. When R. Steiner looked for a new architectural expression of the relationship between the earthly and the Spirit, he chooses the double dom, a metamorphosis of the egg form, see the linked images