The natural man is, speaking in terms of conscious vision, an imaginative seed. Just as the seed is a dry sealed packet of solid "matter," so the natural mind is a tight skull-bound shell of abstract ideas. And just as the seed is surrounded by a dark world which we see as an underworld, so the physical universe, which surrounds the natural man on all sides, and is dark in the sense that he cannot see its extent, is the underworld of the mind, the den of Urthona, the cave of Plato's Republic. The majority of seeds in nature die as seeds, and in human life all natural men, all the timid, all the stupid and all the evil, remain in the starlit cavern of the fallen mind, hibernating in the dormant winter night of time. They are embryos of life only, infertile seeds, and die within the seed-world. The possibility of life within them remains in its embryonic form of abstract ideas, shadows and dreams. Some of the dreams are troubled visions of the real world of awakened consciousness; others are the nightmares of paralyzing horror which all minds in a stupor of inertia are a prey to. Here and there a seed puts out a tentative shoot into the real world, and when it does so it escapes from the darkness of burial into the light of immortality. Such a seed, however, would only have begun its development, for the vegetable life is not the most highly organized form of life, because it is still bound to nature. The animal symbolizes a higher stage of development by breaking its navel-string, and this earth-bound freedom of movement is represented in our present physical level.

The bird is not a higher form of imagination than we are, but its ability to fly symbolizes one, and men usually assign wings to what they visualize as superior forms of human existence. In this symbolism the corresponding image of nature would be neither the seed-bed of the plant nor the suckling mother of the mammal, but the egg, which has been used as symbol of the physical universe from the most ancient times...In Blake the firmament is the Mundane Shell, the indefinite circumference of the physical world though which the mind crashes on its winged ascent to reality. To the inexperienced eye the egg appears to be a geometrical stone, but the imagination within the egg soon demonstrates that it is something much more fragile. The same is true of the Newtonian universe, the rock rolled against the tomb of divine humanity.