The great thousand worlds are just the one true dharmadhātu

Material form does not arise and perish by itself. If material form could arise and perish by itself—arising on its own and automatically perishing on its own—that would mean that material form has a truly existing self-nature. If material form had a self-nature, then it would not need the tathāgatagarbha to manifest and sustain its existence; material form would not be produced and upheld by the tathāgatagarbha, and then there would be places where the tathāgatagarbha does not pervade.

So where does material form actually come from? There must be some source. Even if it fell from the sky, that would still be a source—but such a source cannot possibly exist, because if things could fall from the sky, if the sky could produce material form, then it would not be the sky. Searching high and low, we find that only the tathāgatagarbha can produce material form, because the four great seeds of the tathāgatagarbha can generate matter. All other dharmas are produced by the tathāgatagarbha and none of them can in turn produce material form.

After these material forms are produced by the tathāgatagarbha, the tathāgatagarbha continues to uphold the material forms it has produced, and therefore material forms exhibit the phenomena of arising, ceasing, and change. Moreover, they arise, cease, and change moment by moment: the tathāgatagarbha must constantly transmit the four great seeds moment by moment, continually altering the material forms, so that matter gradually changes and finally disappears. The tathāgatagarbha pervades all places and all dharmas; there is no dharma that is not upheld by the tathāgatagarbha. Without the tathāgatagarbha's upholding, no dharma whatsoever could exist. The tathāgatagarbha has nowhere it does not pervade; therefore the entire great trichiliocosm is the one true dharmadhātu.

Most of the time, when our merit is insufficient and our conditions are not ripe, we easily let slip a very profound sentence hidden in the Buddhist sūtras, dismissing it as ordinary, commonplace language. Yet everyone must cultivate for one incalculable eon, two incalculable eons, or even three incalculable eons before truly awakening to the full meaning of that sentence. As for the four characters "one true dharmadhātu," we must cultivate for three incalculable eons before we can thoroughly understand them. The difference lies in each person's conditions in various respects—merit, meditative concentration and wisdom, mental disposition, and so on. Cultivate more merit and more meditative concentration; subdue afflictions and innate afflictive obstructions as much as possible; make the mind gentle and pliant; gradually remove the "self" from within the mind—remove it again and again, subdue it again and again—and one can realize the selflessness of both person and dharmas. Although this is extremely difficult to accomplish, we must still strive to do it.