Hīnayāna Scriptures Implicitly Discuss the Mindfulness Mental Factor of the Manas

The first of the seven factors of enlightenment is the mindfulness factor of enlightenment (smṛti-saṃbojjhaṅga). 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 of enlightenment, the mindfulness factor of enlightenment cannot be accomplished, and the investigation-of-dharmas factor of enlightenment (dharma-pravicaya-saṃbojjhaṅga) 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 only because sentient beings are heavily obscured by ignorance that they cannot understand the Buddhist sūtras and are unable to discern this.