In the Mahāsatipaṭṭhāna Sutta, when the Blessed One expounded on the five aggregates subject to clinging, he also addressed the internal and external aspects of form, feeling, perception, formations, and consciousness. Internal form is the physical body; external form is the six dusts (sense objects). Internal feeling, perception, formations, and consciousness pertain to the mental faculty (manas), while external feeling, perception, formations, and consciousness pertain to the consciousness (vijñāna).
When the Blessed One taught the seven factors of enlightenment, he also divided them into internal and external seven factors. The enlightenment factors of investigation of phenomena (dhamma vicaya), energy (vīriya), rapture (pīti), tranquility (passaddhi), concentration (samādhi), and equanimity (upekkhā) are each divided into the external factors pertaining to consciousness and the internal factors pertaining to the mental faculty. Without cultivating the internal seven factors of enlightenment to fruition, it is impossible to attain the fruits of the Śrāvaka vehicle, impossible to eradicate the view of self, without even mentioning realizing the mind and perceiving true nature. If the thirty-seven aids to enlightenment are not perfected, there can be no discussion of attaining any fruit, whether of the Great or Small Vehicle. Without achieving physical and mental tranquility, without achieving concentration, without the existence of internal equanimity, it is impossible to eradicate the view of self, impossible to realize the mind and perceive true nature. These are the hard criteria for verification in the practice of the Dharma; no one can bypass them. If one insists that someone has attained the fruit or realized the mind, those are merely plastic fruits, fit only for viewing; they cannot satisfy hunger and possess no real value.
Judging from the Blessed One's description of the seven factors of enlightenment, the mental faculty possesses the enlightenment factor of investigation of phenomena, the enlightenment factor of energy (true diligence), the enlightenment factor of rapture (indicating the mental faculty is not limited to equanimity alone), the enlightenment factor of tranquility, the enlightenment factor of concentration (being associated with concentration), and the enlightenment factor of equanimity. Only after the mental activities accord with the Noble Eightfold Path can the conditions for attaining the fruits of the Śrāvaka vehicle be fulfilled, enabling the eradication of the view of self and the realization of the first fruit (Sotāpanna). Otherwise, they are all false fruits, plastic fruits. When conditions are not fulfilled, when causes and conditions are insufficient, forceful guidance can only yield a false fruit.
Among the seven factors of enlightenment, there is the enlightenment factor of investigation of phenomena. When one cultivates to this stage, one gains discernment. However, when matters far exceed one's current level, the ability to discern is lost again, so one must continue practicing. The enlightenment factor of investigation of phenomena must be continuously enhanced until it is perfectly complete, enabling one to immediately and correctly investigate all phenomena without doubt.
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