The Internal and External Mind in the Mahāsatipaṭṭhāna Sutta

When the Buddha taught about the five hindrances in the Great Mindfulness Sūtra (Mahāsatipaṭṭhāna Sūtra), He spoke of inner greed and outer greed, inner anger and outer anger, inner sloth-and-torpor and outer sloth-and-torpor, inner restlessness-and-remorse and outer restlessness-and-remorse, and inner doubt and outer doubt. What do "inner" and "outer" respectively refer to?

If the mind is divided into inner and outer, the outer mind refers to the mind consciousness that sentient beings can generally discover and observe, while the inner mind refers to the mind root (manas) that sentient beings find difficult to discover and observe. The two conscious minds are one manifest and one hidden, one bright and one dark, one deep and one shallow; one is easily changed, the other is firm and hard to change. Cultivation means first putting practice into effect at the shallow level of the mind consciousness, and then at the deep level of the manas—first preliminarily transforming the mind consciousness, and ultimately and completely transforming the manas. Therefore, all afflictions and ignorance are, at first and most evidently, at the level of the mind consciousness, and, in the end and most hidden and profound, at the level of the manas.

From this sūtra, we can see that when the Buddha taught the Small Vehicle dharma, although He did not explicitly speak of the dharma of the manas, He still implicitly touched upon it—implicitly teaching that all afflictions and ignorance belong to the manas, that eradicating afflictions means eradicating the afflictions of the manas, that liberation is the liberation of the manas, and that all dharmas must be put into effect upon the manas. If one resolves the problem of the manas, one can resolve all dharmas, and ultimately and completely attain nirvāṇa and liberation.