The Red Priests think mass is sinful and so strive to suppress it in both its material and spiritual forms. Huge construction projects, trans-spherical immigration, fat people. Bring down the towers, they say.
The million spheres are exactly that. Mostly that. As long as you bear in mind that you are talking about a multi-dimensional object expressed on a three dimensional plane. They look like spheres from a distance and behave as such. Mostly.
The Nothing, Chaos, The Demon Sea, whatever you call it, is a two dimensional plane. If a theurgist were trying to school a bumpkin on metaphysics he would demonstrate the interaction of the spheres and of the nothing by dropping an apple into a trough of water. He may hammer nails of chaos into it and cause it to sink further, or lift it gently with his (comparatively) hyper-finger. Beneath the water are hungry larvae, who eat the apple. Above the sea is a tree with bare branches.
The Nothing is an inverted sphere, inside of which the spheres float like lights on the water.
A plane intersecting a spherical surface will appear as an angled wall. Cunning scholars can detect the objective nothingness of a sphere by measuring the exact angle.
Horizon Knights are some of the only people to travel via the nothing between spheres, protected in their hermetic keeps. The sensible traveller rides across the humpbacked sky.