Those who dwell upon the earth are the parts of a person fixed in the flesh, the faculties bound to the body and its ground, and their worship of the beast is the whole lower nature bowing to appetite and outward power. The book of life is the inner record of the awakened, the register of those energies in a person that have been raised into consciousness and belong to the living spirit. Names not written in it are the powers that remain unconscious, never lifted out of the animal state. The Lamb slain from the foundation is the pure spirit given up into flesh at the very beginning, the innocent life sacrificed the moment it entered the body of the world.
So the whole passage divides a person into what has been awakened and what still sleeps in the flesh, the one written in the living record and the other still bowing to the beast.
Earth: the flesh and its ground, the fixed bodily nature to which the lower faculties cling
Beast: the animal power of appetite and outward force that the unawakened self worships
Book of life: the inner record of the energies raised into consciousness and joined to the living spirit
Lamb: the pure innocent spirit given into flesh from the beginning, the life sacrificed on entering the body