What kind of practice is one whose merit is not in vain?

Elderly people, due to brain atrophy, have weakened supreme faculties (indriya), and the functions of the six consciousnesses are thereby affected. What are these effects? For example, when an elderly person meets someone new, they remember them at the time but forget afterwards—this is because the mind consciousness's power of recollection and recognition has declined. Is the function of the manas affected? The manas's own function is not affected, but its function of cooperating with the six consciousnesses is influenced by the six consciousnesses, not by the brain or the supreme faculty. This is because when the elderly person saw that person, the impression did not penetrate deep into the manas but remained only at the level of the mind consciousness, causing them to forget afterwards.

However, an elderly person may have a deep impression and profound memory of their close relative A, and may even constantly worry about them in their heart. Even so, sometimes upon seeing A, they clearly know in their mind that it is A, yet when they open their mouth they call out B's name, while still talking about matters concerning A. This is because the mind consciousness has become somewhat muddled, but the manas has not. The older a person gets, the weaker the function of the supreme faculty becomes, and the more muddled the mind consciousness becomes. Although the manas is not muddled, bodily, verbal, and mental actions are all carried out jointly by the mind consciousness and the five sense consciousnesses, so various kinds of confusion and obstruction are inevitable.

In our Buddhist practice, in order to ensure that our efforts are not in vain and that the merit of our practice is not lost, how should we cultivate? We should not remain at the level of the mind consciousness's understanding, deliberation, analysis, recitation, and memorization, but should strive to develop meditative concentration (samādhi), contemplate within that concentration, and steep the Dharma we have learned into the mind of the manas; then, within samādhi, let the manas deliberate (manasikāra) upon it, attaining realization through direct perception. Only by making full use of the manas can we develop genuine wisdom, allowing wisdom to grow continuously, extending into future lives, being enjoyed life after life, growing life after life, and ultimately reaching perfect buddhahood.