[3] and all men who have studied philosophy in a genuine spirit, showing themselves obedient to this injunction, have looked upon it as a sentence, or rather as a law of equal weight with a divine oracle; and, departing from the common opinions of men, they have cut out for themselves a new and hitherto untravelled path, inaccessible to such as have no experience of wise maxims and doctrines, building up systems of ideas, which no one who is not pure either may or can handle.