Why Distinguish the Functions and Roles of the Manas and the Mind Consciousness?

When both hands need to move together, they must be coordinated and act in unison for the movement to be carried out; otherwise it is difficult. The same is true of the two eyes, two ears, two nostrils, two feet, and two legs: they must move in coordination, with the same or similar aims, in order to accomplish things easily; otherwise it is not easy to perform non-unified movements. Why is this? The movements of the two hands are commands issued by the brain, and the brain is directed and controlled by the manas. When the manas wants to use the hands to do something, it issues a command, and the two hands must act simultaneously. If the manas wants to use the left and right hands to do two different things at the same time, the commands transmitted by the brain must be split into two parts, and the mind consciousness and body consciousness must be divided into separate streams; the nervous system then has to strain to cooperate—unless one has undergone a period of special training.

Yet no matter how the two eyes are trained, they cannot each make contact, each apply attention (manaskāra), and each discern separately; it is very hard to separate them. The two nostrils are also very hard to separate—one exhaling and one inhaling—though perhaps it is possible with special training. The two ears are relatively easier to separate in their activities. It is also rather difficult for the two feet and two legs to carry out separate, uncoordinated activities on their own. The reason it is difficult is that they belong to one faculty, one nervous transmission system, one brain command. The ease or difficulty depends on whether the manas has sufficient attention and energy, and also on whether the energy of the six consciousnesses is sufficient.

By separating the functions and roles of the manas and the mind consciousness, one can understand the respective natures of the manas and the mind consciousness better and more clearly; when they are mixed together, the nature of neither consciousness can be understood clearly. Once the functions and roles of the manas and the mind consciousness are separated, and one observes the manas on its own, one can know what characteristics the manas has, what afflictions it has, what habits it has, and what mental factors (caittas) it has; without needing to chew over other people's huatou, one will have the ability to observe the true situation for oneself.