For I do not apprehend the meaning of the God to have been that we should understand our members, our stature, and form; for we are not merely bodies; nor, when I say these things to you, am I addressing myself to your body: when, therefore, he says, "Know yourself," he says this, "Inform yourself of the nature of your soul;" for the body is but a kind of vessel, or receptacle of the soul, and whatever your soul does is your own act.

To know the soul, then, unless it had been divine, would not have been a precept of such excellent wisdom as to be attributed to a God; but even though the soul should not know of what nature itself is, will you say that it does not even perceive that it exists at all, or that it has motion?
On which is founded that reason of Plato's, which is explained by Socrates in the Phaedrus, and inserted by me, in my sixth book of the Republic.
XXIII.

"That which is always moved is eternal; but that which gives motion to something else, and is moved itself by some external cause, when that motion ceases, must necessarily cease to exist.

That, therefore, alone, which is self-moved, because it is never forsaken by itself, can never cease to be moved.

Besides, it is the beginning and principle of motion to everything else; but whatever is a principle has no beginning, for all things arise from that principle, and it cannot itself owe its rise to anything else; for then it would not be a principle did it proceed from anything else.