To observe one's mind is to observe one's own mind, to see how it observes the external world, to see how it functions, to see whether it is pure or polluted, to see whether it has any afflictions or delusions. If the mind that observes is pure and unpolluted, it can know all the external world as it really is; if the mind that observes is polluted, it cannot know all the external world as it really is.

Therefore, looking inwards at one's mind means looking within oneself, seeking truth from within, and exploring the truth in the depths of one's own soul. Another way to look at one's mind is to look outwards at one's surroundings. Looking outwards at one's surroundings means looking at the external world as an object, to see whether it is real or empty, whether it is permanent or impermanent, whether it is self or no self.

By observing the external world, we can further understand the inner state and understand the truth more deeply. Therefore, observing the mind is actually a way of internal and external cultivation, which requires observing both the inner mind and the external world.