Conjecture and Speculation Are Completely Unreliable Methods of Practice

Because sentient beings have limited wisdom and cannot deliberate deeply, and because their meditative concentration (samādhi) is insufficient, the deliberation (manasikāra) of the manas also cannot operate. For some of the deeper dharmas, they habitually resort to conjecture and speculation, and conjecture and speculation are functions of the mind consciousness, containing not the slightest wisdom of the manas. 

The most serious form of conjecture and speculation is to talk carelessly, claiming that after enlightenment one can observe how the eighth consciousness gives birth to the faculties, the body, and the material world. The "faculties" (根) refers to the bodily faculties, the physical body. As for how the eighth consciousness uses seeds to give birth to the bodily faculties bit by bit, and how it gives birth to the eye faculty, ear faculty, nose faculty, and tongue faculty, after enlightenment one may need to cultivate for another innumerable kalpa before perhaps observing a little, and after two innumerable kalpas one could probably observe quite a lot. The "world" (器) refers to the material universe, the container world—the spatial environment in which sentient beings live. As for how the eighth consciousness uses seeds to give birth to the material universe and the container world, after enlightenment one may cultivate for another innumerable kalpa and still perhaps not observe it; after two innumerable kalpas one could probably observe some of it. The "realms" (界) refer to the eighteen realms—the six faculties, six sense objects, and six consciousnesses. As for how the eighth consciousness uses seeds to give birth to the six faculties and six sense objects, even after enlightenment and cultivating for another innumerable kalpa it would still be very difficult to observe; after two innumerable kalpas one could probably observe some of it. As for how the eighth consciousness uses consciousness seeds to give birth to the six consciousnesses, after enlightenment and cultivating for another innumerable kalpa one could observe some of it, but not observe it completely and fully. 

But no matter what one can observe, if one's own mind is not thereby changed, and one's bodily, verbal, and mental actions do not change as a result of this observation, then the so-called observation is not observation at all, but conjecture and speculation. Conjecture and speculation are all methods of the mind consciousness's thinking, not involving the manas at all, so what is conjectured and speculated has no force of effect, and cannot in the slightest purify the mind or transform one's bodily, verbal, and mental actions.