The mind not subject to birth and death is stirred by the wind of ignorance to give rise to birth and death. Therefore the text says that the mind subject to birth and death is based on the mind not subject to birth and death. Still, even though there are these two aspects of the one mind, there are not two separate essences. It is only in terms of theses two aspects of the one mind that the text is able to explain the dependence of phenomenal appearances. It is just like the case of unmoving water that is blown by the wind to become moving water. Even though stillness and motion are different, the essence of water is one. The intrinsically pure mind is called the tathagatagarbha. It is stirred by the wind of ignorance to give rise to birth and death.

- Fa-tsang commentary on the Awakening of Faith