This poem was written by Master Huineng, the sixth ancestor of Zen Buddhism.
Meaning: Bodhi was originally a metaphor of wisdom, and the mirror is like meditation. Originally quiet, where will it be contaminated with dust? The purpose is to explain that everything is like a dream bubble, and to teach people not to think about persistence, to have a clear mind, and to have a self-certified Bodhi.
This poetry is "everything is empty", and this field reflects that all beings have enough "vacuum", that is, "emptiness" and "heart" that is not immortal or foreign.
Extended data:
The Diamond Sutra says, "Buddha says that Buddhism is not Buddhism, but Buddhism."
The bodhi tree is not bodhi, it is called bodhi, and the stage is not a stage, but a stage. The heart is not attached to the appearance, and there is nothing. There is no pollution and dust in the heart of nature.
It can't be understood as emptiness here, because the bodhi tree and the stage are real, and it should be understood as "emptiness" in the heart without clinging to foreign objects.
Therefore, it is said that "all methods return to the heart", and practicing Buddhism is to cultivate the heart.
References:
Baidu encyclopedia-bodhi without trees (one of the four sentences of master Huineng, the sixth ancestor)