The functions of the seeds of tathāgatagarbha can only be directly realized by bodhisattvas who have attained the bhūmis.

All dharmas of the five aggregates and eighteen realms are the nature of the tathāgatagarbha. This principle can only be gradually comprehended through contemplative practice (vipaśyanā-caryā) after personally realizing the tathāgatagarbha. If one merely imagines with the mind consciousness that there is a tathāgatagarbha performing certain functions, then there is no way to observe the operation of the tathāgatagarbha, and no way to observe the tathāgatagarbha nature of the five aggregates and eighteen realms. Understanding is, after all, merely understanding; imagination is, after all, merely imagination—it is not personal realization. How the tathāgatagarbha records and stores seeds, and how it brings about cause and effect—these belong to the seed-wisdom of Consciousness-Only, which only bodhisattvas who have attained the bhūmis can observe through direct perception. The seed functions of the tathāgatagarbha, its function of manifesting the myriad worldly dharmas, and all of the tathāgatagarbha's seed functions belong to the domain of the seed-wisdom of Consciousness-Only, which only bodhisattvas who have attained the bhūmis can observe through direct perception. Pre-bhūmi bodhisattvas (pūrvabhūmika bodhisattvas), because their afflictions are heavy and their meditative concentration (samādhi) is insufficient, lack sufficient wisdom; since the sixth and seventh consciousnesses have not undergone the transformation of consciousness into wisdom, they lack the power to observe these extremely profound and subtle dharma principles. What is merely understood cannot substitute for direct observation.