Marsilio Ficino’s Platonic Theology, Volume II

4For if they move in a circle, their motion never ceases. Circular motion does not let its powers flow away; instead, it gathers all that belongs to it back into itself, and when it seems to fail, it renews itself. I pass over for the present Pythagoras's argument, which shows that a sphere has neither beginning nor end, and therefore that whatever is carried in a spherical circuit neither ever began to move nor ever ceases.

5That argument further shows that rational souls are certain spiritual spheres and trace within themselves a spiritual circuit, since the bodies themselves, which are their shadows, possess just such a figure and motion. Thus visible spheres and circuits are shadows of invisible spheres and circuits. And if the shadows are perpetual, much more must those substances be perpetual, for through a power without limit they sustain the act of motion without limit. Nor is there anything contrary to them that could destroy them, just as their own circular motion has no contrary motion.