The first experience of the mystic is that existence is not a problem but a mystery; it is unknowable – not only unknown. Science divides existence into two categories: the known and the unknown. Hence science assumes that a day is bound to come when the whole unknown will be transformed into the known. That will be the end of all inquiry.
But religion believes in three categories. The known and the unknown belong to the lower world of knowledge, and the unknowable belongs to the higher world of knowledge. That higher will always remain the same; it will be always there to inquire into, to go into; to merge with, to melt into, to become one with.
Lao Tzu says: “Knowing the not-knowing” – knowing that life is absolutely mysterious, that there is no way to know it – “that is high.” That is the ultimate of experience. There is no beyond to it, nothing more transcendental than that; one has arrived home. The moment you enter the mysterious, you have found the home. No knowledge can satisfy you unless you are merged with the unknowable. “Not knowing the knowing – that is an illness.” Lao Tzu calls even wisdom an illness, because you are falling from the ultimate health, ultimate well-being. “Not knowing the knowing….”
Even by saying, “I don’t know,” you have asserted something, you have said something, you have claimed some knowledge. For example, if Socrates had met Lao Tzu, Lao Tzu would have said, “You are ill – ill with wisdom! A good illness, but you are just a step below,” because Socrates’ famous statement is: “I know only one thing, that I know nothing.” But there is a claim: “I know.” Although the claim is that “I know nothing,” still it is a claim of knowing, a claim of knowledge. Even though it claims that life is mysterious, the claim has come in.
Even to say that God is indefinable is a kind of definition. To say that truth is inexpressible is in a certain sense giving it some expression. To say that the truth cannot be said means you have said something about it. Your very statement falsifies it; it is self-contradictory. Hence he calls it illness – it is self-contradictory.