Excerpts from the Śūraṅgama Sūtra

Original Text: The nature of form is true emptiness; the nature of emptiness is true form. The nature of water is true emptiness; the nature of emptiness is true water. The nature of fire is true emptiness; the nature of emptiness is true fire. The nature of wind is true emptiness; the nature of emptiness is true wind.

Explanation: The earth, water, fire, and wind of the material universe are composed of the seeds of the four great elements from the Tathāgatagarbha. Therefore, the nature of earth, water, fire, and wind is the nature of these four great seeds. The four great seeds are formless and empty; hence, earth, water, fire, and wind are emptiness in nature. The nature of the four great seeds is the Tathāgatagarbha nature; thus, the nature of earth, water, fire, and wind is the Tathāgatagarbha nature, which is the wondrous true suchness nature. Because the Tathāgatagarbha contains the seeds of the four great elements, these seeds can generate the earth, water, fire, and wind of the material universe. Earth, water, fire, and wind are the Tathāgatagarbha nature, transformed by the Tathāgatagarbha using the four great seeds. Therefore, the Tathāgatagarbha contains the nature of earth, water, fire, and wind and possesses their characteristics. The Tathāgatagarbha is not earth, water, fire, or wind, yet it is earth, water, fire, and wind. The Tathāgatagarbha and earth, water, fire, and wind are neither identical nor different.

"Nature-emptiness" refers to the emptiness nature of the Tathāgatagarbha. All phenomena born from the Tathāgatagarbha are empty and unreal in nature, generated by the outflow of a portion of the Tathāgatagarbha's seeds. Thus, a portion of the Tathāgatagarbha becomes form, and the essence of all form dharmas is the true emptiness mind—the Tathāgatagarbha. The emptiness mind Tathāgatagarbha can produce all forms; therefore, all forms are also the Tathāgatagarbha nature. "The nature of form is true emptiness" means the essential nature of form is the Tathāgatagarbha, the true emptiness mind Tathāgatagarbha nature. This is slightly similar to the phrase in the Heart Sutra: "Form is emptiness; emptiness is form." Similarly, water, fire, and wind share this same relationship with the Tathāgatagarbha.