The sutras teach that ordinary people, sages and saints are all equal. There is no difference [in their intrinsic nature]. Only the defilement or purity of mind is different. For this reason, it is said that “Mind, Buddhas and sentient beings are no different from one another.” A Pure Mind is Buddha, a defiled mind is sentient being. Buddhas and sentient beings differ only in the extinction or non-extinction of defilements of the mind.
The mind is inherently clean and pure, but it is obstructed by greed, hatred, stupidity, arrogance, the five desires and many kinds of delusions. Therefore, those with such minds are called sentient beings. If defilements are discarded and the mind becomes pure, that is Buddhahood. It is not necessary to depend on others.
However, all sentient beings bear heavy karma and stubborn afflictions from time immemorial, and these are very difficult to purify. To do so requires cultivation, such as [serene, reflective] meditation, working on a hua-t’ou [koan] or Buddha Recitation. So you see, there are many expedient ways to practice, but all are medicines to treat the diseases of the mind. For example, a mirror, intrinsically bright, cannot reflect anything if it is covered with dust. To restore its brightness, a cleaning agent (remedy) is required. Yet the cleanser itself is also dust, though it can rid other things of dust. Once the mirror is bright, there is no further need for the cleanser. This is like gold in its ore, covered with the dirt and dust of sand and stone. After it is smelted and pure gold appears, there is no need to smelt it again.
It is difficult to rid oneself of the defiled mind characteristic of sentient beings. However, it can be done through diligent practice. When this is accomplished, the bright and undefiled mind appears. It is in this sense that all sentient beings are said to be inherently Buddhas.
~ Master Han-Shan’s Dream Roamings, Trans. by Master Lok To