There is a great gap between intellectual understanding and realization.

If one sees that all marks are not marks, then one sees the Tathāgata. If someone understands it this way—regarding everything they perceive (like the content displayed on a television screen), being able to constantly and everywhere recognize that all of it is the illusory transformation of the substances and functions within the tathāgatagarbha (like the television screen)—does that mean this person has realized the tathāgatagarbha? Not at all; they are still far from it. Between hearing and imagination and actual realization there remains a very, very great distance, and the gap between them is the bodhisattva's practice of the six pāramitās.

All of the above is the mind consciousness's crudest, most superficial understanding, similar to hearsay—except that it is heard from the Buddhist sutras, or from some book—and it has not been actually realized; it is not something observed through direct perception. No matter who says it, it still counts as mere understanding. When it is truly and actually realized, who knows what bhūmi bodhisattva one would be. Those contents are spoken of in the sutras, and others speak of them too; things spoken by others do not belong to one's own personal realization. With personal realization, one knows very concretely and precisely, not in a general, approximate, or vague way. To realize what specific role the tathāgatagarbha plays in the five-aggregate body, one must go through Chan investigation, actually putting in the effort to investigate, groping and exploring bit by bit through the intermediate process. If one does not do the work, relying only on one's feelings and guesses, understanding just a little, then in reality one has no idea what specific role the tathāgatagarbha plays—one is completely in the dark. Then all ignorance remains intact, and no wisdom is born.

Believing that all dharmas are like the content within a television screen is belief, not realization or firsthand realization; it cannot be called realization, because there is no evidence. Believing that all dharmas are created by the tathāgatagarbha and that we all live in the one true dharmadhātu—this is not enlightenment. If a single sentence from the Buddha could let sentient beings attain enlightenment so easily, the Buddha-dharma would be far too easy: even a three-year-old child who heard this sentence and roughly understood a bit of it would count as enlightened. Then how effortless becoming a Buddha would be! The karmic obstructions of birth and death over countless kalpas upon countless kalpas could not obstruct anything, and all that ignorance would count for nothing. In reality, nothing so easy exists.

Without going through Chan investigation, without investigation and gathering of evidence, without collecting data and proof, how could the manas confirm that these teachings are the truth and accept them with faith? Genuine awakening to the truth requires knowing the details of how the eighth consciousness operates—specifically how it gives rise to all dharmas, how it gives rise to sentient beings' five aggregates and eighteen elements—all of this must be understood and known, and all six pāramitās of the bodhisattva must be cultivated. It is not a matter of understanding some portion of the content; those portions were spoken by the Buddha or by others, and no matter how one understands and elaborates on them, it is not something one has personally pondered, investigated, and realized through one's own verification. Without direct observation, the mind does not settle; it remains hollow and insecure. Between this kind of understanding and realization, perhaps one year is needed, perhaps thirty years, perhaps a hundred years, perhaps ten thousand years, perhaps a whole incalculable kalpa—there is no telling. What the mind consciousness understands is useless; it vanishes the moment it vanishes. Even the mind consciousness itself does not know or realize the details, let alone how the manas could know and realize them. At the critical moment, it is still the manas that makes the decisions. If the manas has not confirmed it, ignorance remains, and all the mind consciousness's understanding, at the time of death, is like a child's play—dissolving into bubbles, unable to determine the destination of the next life.

Ask yourself "why" often in your mind, and answer every one of those whys—perhaps that brings you close to the edge of realization, but it is still not necessarily realization. Such is the Buddha-dharma: sacred and beyond speculation.