The Tao which can be expressed in words is not the eternal Tao; the name which can be uttered is not its eternal name. Without a name, it is the Beginning of Heaven and Earth; with a name, it is the Mother of all things. Only one who is eternally free from earthly passions can apprehend its spiritual essence; he who is ever clogged by passions can see no more than its outer form. These two things, the spiritual and the material, though we call them by different names, in their origin are one and the same. This sameness is a mystery, -the mystery of mysteries. It is the gate of all spirituality.