The Altar Sutra: Dhyana
The Patriarch gave this teaching:
In our system of meditation we don't dwell on the mind nor do we dwell on purity. Also we are active. As to dwelling on the mind, the mind often leads us to delusion. When we realize this, there is no need to dwell on it.
As to dwelling on purity, our true nature is pure, so there is no reason to dwell on it. Dwelling on purity is to create a problem where none exists. On another occasion the Patriarch gave this teaching:
What is sitting in meditation? In our school, to sit means to gain freedom and to be mentally undisturbed by outward circumstances. To meditate means to sit, dwelling in our Buddha nature.
What are Dhyana and Samadhi? Dhyana means to be free from attachment to outer objects and Samadhi means to have inner peace. If we are attached to outer objects then our minds will be disturbed. When we aren't attached to outer objects, our minds are in peace. Our true nature is pure and the reason we are disurbed is because we allow ourselves to be carried away by circumstances and external objects.
One who is able to keep the mind undisturbed regardless of circumstances dwells in Samadhi.
To be free from attachment to outer objects is Dhyana and to attain inner peace is Samadhi. When we are in a position to relate to the world in Dhyana and to keep our minds in Samadhi, then we have attained Dhyana and Samadhi.
The Bodhisattva Sila Sutra says, "Our Essence of Mind is intrinsically pure."
Let us realize this for ourselves and train ourselves to practice it and attain Enlightenment.