The Implicit Teaching on the Mental Factor of Mindfulness of the Manas in the Nikāya/Āgama Sūtras

The first of the seven factors of enlightenment is the mindfulness enlightenment factor (smṛti-saṃbodhyaṅga). The internal mindfulness factor is the mindfulness of the manas, while the external mindfulness factor is the mindfulness of the mind consciousness. When the manas lacks the mindfulness factor, the mindfulness enlightenment factor is not accomplished, and the dharma-investigation enlightenment factor cannot manifest. Therefore, the manas definitely possesses the mental factor of mindfulness. The Hīnayāna sūtras already implicitly speak of the manas's mental factor of mindfulness, let alone the Mahāyāna sūtras. It is merely that sentient beings, heavy with ignorance, cannot understand the Buddhist sūtras and are unable to discern this.