The Godsveil & the Nature of Shadow

Shadow leaks into our world from the Endless Void. It is the essence of the Great Old Ones of Yuggoth, whose minds are unknowable, and who are ancient compared even to the gods. The Shadow feeds off the dance of light and darkness. It is a perversion of nature, and maddening of mind, an ineffable malignancy creeping like a spreading stain that has no regard for the lives of mortals. The Old Ones were banished to the darkest recesses of this world, and other worlds of the material plane, through the self-sacrificing efforts of the Elder Gods, and even the Devils of the Nine Hells, who managed to spin fragments of the Godsveil to envelop these alien beings in eternal prisons here upon Shenn.
It is the Godsveil that keeps the gods, demons and devils of the Outer Planes out of our material realm. In effect, all are banished beyond the Veil, condemned to their own planar realms. But their influence remains in our world, leaking through by way of prayer, light, sacrifice, bloodshed or disturbances such as fear and anger. The gods and Dark Ones touch us in many ways. Some even manifest parts of their beings as mortal avatars, subject to the natural laws of our world, but the gods themselves cannot pass through the boundary.
The Godsveil itself is like a fine net of unbreakable thread, unimaginably vast, spun by the Norns (known as Fateweavers) and placed around our dimension in order to preserve it from such powerful entities. It wraps around the astral plane and forms a kind of membrane between the realms of the gods. The gods, and their counterparts the demons and devils, can breathe into this world, can make their presence known and felt, but they cannot themselves manifest here. For if such beings of opposing domains should converge upon one plane, that place would surely be ripped apart by the chaos that ensued.