The Tao that can be understood cannot be the primal, or cosmic, Tao, just as an idea that can be expressed in words cannot be the infinite idea.
And yet this ineffable Tao was the source of all spirit and matter, and being expressed was the mother of all created things.
Therefore not to desire the things of sense is to know the freedom of spirituality; and to desire is to learn the limitation of matter. These two things spirit and matter, so different in nature, have the same origin. This unity of origin is the mystery of mysteries, but it is the gateway to spirituality.