Excerpts from the Śūraṅgama Sūtra

Original text: 性色真空，性空真色；性水真空，性空真水；性火真空，性空真火；性风真空，性空真风。

Explanation: The earth, water, fire, and wind of the universe's material world (器世间) are composed of the four great-element seeds of the tathāgatagarbha, so the nature of earth, water, fire, and wind is precisely the nature of the four great-element seeds. The four great-element seeds are formless and markless, being empty; therefore earth, water, fire, and wind are emptiness (śūnyatā). The nature of the four great-element seeds is the nature of the tathāgatagarbha; therefore the nature of earth, water, fire, and wind is the nature of the tathāgatagarbha, that is, the wondrous true suchness nature. Because the tathāgatagarbha contains and stores the four great-element seeds, and the four great-element seeds can generate the earth, water, fire, and wind of the universe's material world, and since earth, water, fire, and wind are the nature of the tathāgatagarbha—transformed by the tathāgatagarbha through the four great-element seeds—it follows that the tathāgatagarbha contains the nature of earth, water, fire, and wind, and also possesses their properties. The tathāgatagarbha is not earth, water, fire, and wind, yet is precisely earth, water, fire, and wind; the tathāgatagarbha and earth, water, fire, and wind are neither identical nor different.

"Emptiness of nature" refers to the emptiness (śūnyatā) of the tathāgatagarbha. The myriad dharmas born of the tathāgatagarbha are empty in nature and not real; they are generated by a portion of the tathāgatagarbha's seeds flowing forth. Thus a portion of the tathāgatagarbha becomes form, and so the essence of all material form (rūpa-dharma) is the true emptiness mind, the tathāgatagarbha. The emptiness mind, the tathāgatagarbha, can produce all forms and appearances; therefore all forms and appearances are also the nature of the tathāgatagarbha. "The nature of form is true emptiness"—the nature and essence of forms and appearances is precisely the tathāgatagarbha, the true emptiness mind, the tathāgatagarbha nature. This is roughly the same as the statement in the Heart Sutra: "Form is emptiness (Śūnyatā); emptiness is form." By the same reasoning, water, fire, and wind stand in this same relationship with the tathāgatagarbha.