‘I think there are many of you who think, “I must not think,” so you suppress thought. This is the worst thing to do. You are suppressing the natural flow of the Dharma itself. Don’t think of trying to suppress thought. By thinking, “Don’t think, don’t think,” your essential nature is lost. Without any freedom or comfort, you only end up sitting and thinking of trying to get rid of suffering. This is the sickness of not knowing that the thought of getting rid of suffering is suffering.
In order to have you understand this really well, I will say it one more time. Zen is neither thinking nor not thinking. “When there is thinking, there is only thinking, and while thinking, there is liberation.” And “When not thinking, there is only not thinking, and while not thinking, there is liberation.”
Zazen is not something to be learned from a teacher. Zazen is something learned by means of zazen itself. That is why we say, “zazen is zazen.” I would like you to verify this yourselves through “real practice and real inquiry.”‘ (The Essence of Zen)
I have been trying to come up with a good commentary on the lines from the Fukanzazengi that Harada Roshi is dealing with here (‘Think of not-thinking. How do you think of not-thinking? Nonthinking. This in itself is the essential art of zazen’), and this is obviously way better than anything I might have said. He also translated ‘nonthinking’ as ‘leaving thinking as-it-is’, which is less mystifying, and brings to mind Suzuki Roshi’s repeated mentions of ‘things as-it-is’. Internally or externally, letting things be as they are is the gate of liberation.