The tao that can be told is not the eternal Tao The name that can be named is not the eternal Name. The unnameable is the eternally real. Naming is the origin of all particular things. Free from desire, you realize the mystery. Caught in desire, you see only the manifestations. Yet mystery and manifestations arise from the same source. This source is called darkness. Darkness within darkness. The gateway to all understanding.
The tao that can be described is not the eternal Tao. The name that can be spoken is not the eternal Name. The nameless is the boundary of Heaven and Earth. The named is the mother of creation. Freed from desire, you can see the hidden mystery. By having desire, you can only see what is visibly real. Yet mystery and reality emerge from the same source. This source is called darkness. Darkness born from darkness. The beginning of all understanding.
The Tao is like a bellows: it is empty yet infinitely capable. The more you use it, the more it produces; the more you talk of it, the less you understand.