This is the Gatha (Song of Awakening) of Huineng. This is what his teacher read in order to determine his level of Awakening and what caused his teacher to transmit the Dharma to him.
Bodhi originally has no tree.
The clear and bright mirror also has no support.
Buddha-nature is constantly purifying and cleaning,
Where could there be dust?
He wrote this in response to a gatha that a competing student, Shexiu, had written which was:
Body is the Bodhi tree,
Mind is like a bright mirror-stand.
Take care to wipe it continually,
And allow no dust to cling.
So, Huineng’s gatha probably needs to be understood as a response to Shenxiu’s. Shenxiu’s analysis involves conceiving of Enlightenment as something we’re trying to attain. Huineng’s verse is applying the philosophy of Emptiness to the teaching of Enlightenment.
We think of delusion as something that we have to get rid of. The truth is that delusion only has as much meaning as we give to it. We have to recognize that the delusion isn’t there in the first place. If we think of it as a solid thing that we have to clear away, that can make things difficult for us. All we really have to do is realize that it isn’t there, to see through it. We get there by realizing we are already there.
Shenxiu’s view is called the gradual method. In the gradual method one engages in all sorts of expedient means such as chanting and sutra reading. By engaging in these, one gradually attain Enlightenment. This is polishing the mirror.
Huineng’s view is called the sudden method. In his view, since Enlightenment is our true nature, we can touch it right now. It’s not something that has to come slowly, we just have to have the right circumstances to see through our delusion. Huineng heard someone chanting the Diamond Sutra and that was all that he needed to see the Empty Mind Ground.