In fact, there are two poems in total. One from Venerable Shenxiu and one from Venerable Huineng whose poem is in replied to the one from the previous. Here is goes :
身是菩提树 (Shen Shi Pu Ti Shu)
心如明镜台 (Xin Ru Ming Jing Tai)
时时勤拂试 (Shi Shi Qin Fu Shi)
莫使惹尘埃 (Mo Shi Re Chen Ai)
The body is the Bodhi tree
The mind is like a bright mirror stand
Moment to moment, diligently wipe
To let no dust alight
This first verse by Venerable Shenxiu reflects conventional or relative truth as it speaks of form. The body is the Bodhi tree because just as the Buddha depended on the tree for shelter during the quest for enlightenment, we too depend on the body to practise and realise the Dharma. The Buddha once said that Within this fathom long body [i.e. entire length of the body] is the world [that we experience with our senses], the origin of the world, the cessation of the world and the path leading to the cessation of the world. In other words, we depend on this body as a vehicle or instrument to realise enlightenment. (The cessation of the world can be seen as the cessation of suffering. The above quote can be seen as another way of stating how the Four Noble Truths can be realised by mindfulness of all that rises and falls within ones body.)
The mind is like a bright mirror stand because the mind shows us whatever is reflected onto it. Our perception of reality is clouded when there is the dust of defilements (attachment, aversion and delusion) on the mind. Hence, we should be mindful from moment to moment, to not let this dust pollute the mind, to mar our vision of truth. Only with a dust-free mind can the mirror of the mind reflect perfectly, letting us perceive reality completely.
菩提本无树 (Pu Ti Ben Wu Shu)
明镜亦非台 (Ming Jing Yi Fei Tai)
本来无一物 (Ben Lai Wu Yi Wu)
何处惹尘埃 (He Chu Re Chen Ai)
Bodhi originally has no tree
The bright mirror also has no stand
Originally there is not a thing
Where can dust alight?
This second verse by (the later) Venerable Huineng reflects ultimate or absolute truth as it speaks of emptiness (of substantiality). Although the path towards enlightenment (Bodhi) is conditioned by practice, the actual essence of Bodhi is not based upon any tree or any body because Bodhi is unconditioned. Because the true nature of the liberated mind does not abide anywhere, it has no stand. It is due to attachment that the mind dwells upon physical and mental things, including the idea that The body the Bodhi tree and that The mind is like a bright mirror stand. As long as there is attachment to these forms, even in the mind, Bodhi is not realised.
As all mind (symbolised by the mirror) and matter (symbolised by the tree) change from moment to moment, there is no substantial thing which is why Originally there is not a thing. Yet, it is because there is not a fixed thing, that there can be everything in the constant change (other than the unconditioned) of phenomena. As there is no fixed mind and matter, the unsubstantial (also changing) dust of defilements has no substantial place to alight or collect. Only when we have the delusion of fixed mind and matter do we seem to accumulate defilements. But because we accumulate defilements this way, we would need to, from Moment to moment, diligently wipe to let no dust alight. The first verse thus has to be practised till the second verse is realised. To function as a practicing Bodhisattva, one has to relate to the unenlightened using conventional truth (taught in the first verse), while trying to realise the ultimate truth (taught in the second verse). This is the Middle Path of the Bodhisattva that leads to the liberation of one and all.