The Daodejing speaks of the gate to many mysteries (衆妙之門, chapter 1). The title of the Zen text, the Wumenguan, can be translated as the gate to nothingness.
Mystery is clearly what we don’t know by rational means. It cannot be known by the “Dao that can be told.” (Daodejing, chapter 1) We cannot ever know it by language or by desire alone.
It’s still important and part of daily life. Rather than dismissing it as outside our everyday knowledge, we must accept it as the other half of all that we know. Mystery enables this world. It is not somewhere distant but close at hand.
As such, another definition of mystery, that which is profound, comes to the fore here. Profound is that which is intensely important, deep, and all-encompassing in its truth. We prize the profound precisely because it gives insight into existence. It is beyond any means to construct it or grasp it in a fragmentary way. Mystery also means a spiritual truth that one can know by revelation rather than through the intellect.
Tao requires the integration of all approaches to knowledge. This is done through a process of enlightenment rather than philosophical argument or intellectual analysis. It’s only when we have accepted all dualities that we find ourselves ready to enter Tao.
The word gate reminds us of Tao in the sense of “road.” The normal modes of philosophical inquiry have been addressed. We embark through the gate on a journey. We enter the unknown, we enter the other-wordly, we enter the profundity of Tao itself.
We enter mystery on mystery, the most intense and beautiful way to live.