肇論疏 2.23

2.23

第四、明體也。文中有三：初，正明體；次，解釋；後，引兩經證成。今初。言其者，聖智也。物者，謂此聖智之為物性也，此乃非物名為物耳。實而不有虛而不無者，知法皆空，謂之實也；雖言是實，而體性非物，故言不有。體性非物，即名為虛；無所不知，故云不無。亦可言以無知故言不有，無所不知故言不無耳。存而不可論者其唯聖智乎者，不無此智，故言存也。不可論其相貌定有定無，故言不可論也。唯獨聖智如此，故云唯也。

Part four clarifies the essence. In this text there are three sections: first, directly clarifying the essence; next, explaining it; and last, citing two sūtras to establish it. This is the first.
Regarding "its": This refers to sacred wisdom. "Thing" refers to the nature of this sacred wisdom as an entity; this is calling it a "thing" when it is not a thing. "Real yet not existing, empty yet not non-existing": Knowing that all phenomena are empty is called "real." Although it is called real, its essential nature is not an entity, so it is said to be "not existing." Its essential nature not being an entity is termed "empty"; having nothing it does not know, it is said to be "not non-existing." One may also say: because of non-knowing it is said to be "not existing," and because there is nothing it does not know it is said to be "not non-existing."
Regarding "Existing yet impossible to discuss—can it be only sacred wisdom?": Because this wisdom is not non-existent, it is said to "exist." Because its characteristics cannot be discussed as definitively existing or definitively non-existing, it is said to be "impossible to discuss." Only sacred wisdom alone is like this, hence it says "only."