Lectures on the Sūtra of the Collection of the Father and Son (Pitāputrasamāgamanasūtra), Part Ten

Original text: 大王。云何为内地界。谓于内身。所生硬涩。发毛爪齿。皮肉筋骨。若内地界不生。亦无有灭。则无集行。

Explanation: The Buddha said: Great King, what is the internal earth element? The earth element is the earth great seed within the tathāgatagarbha. Because the tathāgatagarbha possesses the earth great seed, it can manifest the hardness of material form, and can transform and produce the living environment of the material world (bhājana-loka) and the physical sense faculties of sentient beings. The internal earth element is the earth great component within the physical body of sentient beings—the hard portions present in the physical body, such as the hair, nails, teeth, skin, muscles, sinews, bones, and other tissues that possess the hard earth nature.

The internal earth element begins to arise when one enters and dwells in the mother's womb. When the manas enters rebirth into the fertilized egg, the tathāgatagarbha outputs the earth great seeds to transform and generate the fetus's physical body; otherwise, the physical body would have no earth great component, and the body would be limp like water, unable to walk, stand, sit, or lie down. Since the earth element has arising, it must have ceasing; with arising and ceasing, the five aggregates body can be accumulated, and there is bodily action. If the earth great seeds do not arise within the physical body, then there can be no ceasing, and the five aggregates body cannot be accumulated. Dharmas with arising and ceasing are false dharmas, not true dharmas; they are illusory dharmas, empty dharmas. Therefore, we must not crave, cling to, or grasp them.