Lokadharaparipṛcchā... wait, the term list gives 父子合集经 → Sūtra of the Collection of the Father and Son (Pitāputrasamāgamanasūtra). 讲记 = lecture notes/commentary. (五一) = (51). Lectures on the Sūtra of the Collection of the Father and Son (Pitāputrasamāgamanasūtra) (51)

The Characteristics of the Space Element

Original text: 大王。若色变坏。一切皆空。所以者何。是虚空界。本无尽故。安静不动。犹如涅槃。遍一切处。无有障碍。

Explanation: Great King, when material form deteriorates and perishes, it becomes nothingness—that is the space element. Why is it that when material form disappears, everything becomes empty? Because the space element is endless and boundless, everything can become empty. And space is by nature tranquil and unmoving, neither arising nor ceasing, neither increasing nor decreasing, like the nature of nirvāṇa. Space pervades all places, and there is no dharma that can obstruct it.

When material things perish, they become empty space. For example, when a house is destroyed, that spot entirely becomes empty space; when the Earth is destroyed, the place where the Earth was entirely becomes empty space; when the trichiliocosm is destroyed, the entire trichiliocosm becomes empty space, with nothing whatsoever in it.

Space is tranquil and unmoving. Why is it unmoving? Because it is an insubstantial fabrication. Material objects are also unreal, yet objects can be moved, whereas no one can move space even a little. If you build a very tall building in space, can you shift the space? Space does not move; no one can move space, because space contains nothing and has no boundaries—how could it be moved? Since there is no material form in space, it is simply nothingness, emptiness. We constantly need space and emptiness in order to move our bodies and place objects, because space has no obstructions; sentient beings need this quality of being without obstruction, for the sake of moving about and storing things.

Some people say that air is also empty and should, like space, be boundless and immovable. But in fact air and space are vastly different. On the surface, air also appears to be without substance—invisible and untouchable—yet instruments can detect the presence or absence of air. Air does contain matter: within it are the various gases we need, all of them material form composed of the four great elements, and therefore air can flow. What sentient beings need from air is, above all, the oxygen it contains.