Why Can a Defiled Manas Only Give Rise to the First Six Defiled Consciousnesses?

Because the first six consciousnesses arise in reliance upon the choices (the volitional mental factor, cetanā) of the manas, they exist for the sake of what the manas needs; whatever the manas needs, the six consciousnesses are born to carry out. Thus, if the manas is defiled, the six consciousnesses will follow along and create defiled karmic actions; if the manas is pure, the six consciousnesses will follow along and create pure karmic actions. According to the fundamental cause of sentient beings' transmigration through birth and death as revealed by the twelve links of dependent origination, it is because the manas has ignorance (avidyā) that, with ignorance as the condition, the manas's volitional formations rooted in ignorance arise; and with the manas's volitional formations rooted in ignorance as the condition, the bodily, verbal, and mental actions of the six consciousnesses rooted in ignorance arise. All these bodily, verbal, and mental actions settle into the Ālayavijñāna and become seeds.

The volitional formations of the manas are precisely the manas's choices and actions. Once the manas makes its choice, the six consciousnesses are born to assist the manas in carrying out its activities. Therefore, if the manas is defiled and has ignorance, the six consciousnesses, acting as its assistants, will help the manas create defiled karmic actions. However, if the manas, though defiled, does not choose defiled actions, the mind consciousness can rely on its own purity to perfume the manas; if the manas permits the pure actions of the mind consciousness, then pure karmic actions will arise. Therefore, cultivation means to habituate oneself to wholesome dharmas and to use these wholesome dharmas to perfume the manas, thereby breaking through the manas's ignorance and transforming the manas. Then the mind becomes pure, and in the future there will be pure karmic virtues to enjoy.