In Genesis there is put great emphasis on building the firmament/expanse/vault (of heaven). In Sumer it was Enlil that seperated his parents An (sky) and Ki (Earth) for creation to happen. In Egypt it is the wind god Shu who keeps Nut (sky) and Geb (earth) seperated. His name means 'emptiness' and 'he who rises up'. It is said that without Shu, Nut and Geb would have continuous sex, mixing light and darkness, creating good and evil (duality) eternally and no physical life could exist.
So in a real sense if you do not occupy this expanse of emptiness between heaven and earth and the truth of heaven is too heavy for you, the sky essentially falls on you and pushes you down in to the earth/underworld and you are stuck in this place where duality exists and good and evil mix continously.
It is becoming light as the 'feather of maat' (truth, justice, peace and harmony) that grants you access to this expanse. Good/heaven above you and evil/darkness below you. It is realizing this 'void'/vault of aether/akash/space within yourself that the buddhists call sunyata (emptiness) and the taoists call Wu (nothingness), the awakening of buddha nature.
It is the core substance of creation inside the firmament. The substrate in which the spirit of God can dwell. Where maat/dharma/cosmic law is upheld. The place where the breath of life exists, like Shu is decked out with ankhs (symbols of life). The end of suffering and where the kingdom of God presides. :) Vayu in hinduism is the one responsible for this 'atmosphere' of vata (space/air elements), holding up heaven (gizmo on the right). The Jade emperor also has this hat that serves the same purpose, that was used by emperors of China or 'sons of heaven' (which is pretty much the same idea as the pharoah). Upholding heaven, ruling the expanse with clarity of mind, guided by the heavens.