Zazen limited to formalized sitting is not real zazen (tso-ch’an). It is ritualized sitting. It is what Zennists do who lack real insight into their true nature; who have never been taught correctly insofar as they believe that keeping the zazen posture, itself, is enlightenment.
When the Sixth Patriarch Hui-neng taught zazen or tso-ch’an it had a different meaning than it has today. The first character “tso” was not sitting in a literal sense. Sitting meant to be unmoved by thoughts; not being mentally perturbed in external circumstances. As far as “ch’an” or zen was concerned, the second character, it meant to inwardly realize our true nature, or the same, the essence of Mind.
In a nutshell, true Zen meditation is all about awakening to our true or Buddha nature which, of course, is not easy to do—but we have to do it. When we sit on a meditation cushion in the proper meditation posture we are not suddenly Buddhas! We have not awakened. We are still ignoramuses. Despite this disheartening reality, we still have what it takes to awaken. We are lacking nothing. Yes, our work is cut out for us. We still have to penetrate perfectly through the rind of our psychophysical body (the Five Aggregates or pañcaskandha) until we reach our true nature.
How then will we know that we have reached our true nature? It is like a person who is slowly dying from thirst in a desert who suddenly discovers an oasis with an abundant supply of water. In somewhat the same way, for aeons we have been thirsting to find our true nature. One day, our Buddha-nature finally meets face to face with itself for the first time after years of confusion and struggle. When this happens there is no tso or ch’an; no zazen or sitting. There is only this luminous nature.
For those who have found their true nature, zazen means nothing. It is like finding a huge vein of gold. Whereas the tools were of great importance before the discovery, after finding such a large vein, their importance dwindles away.