首楞嚴義疏注經 4.554

4.554

舜若多，云空，即主空神也，無色界天亦是此類，隨其所主亦無色質。既為風質者，此約體不可見，故云元無。以佛力故故能暫現，亦顯有定自在色，無業色也。無色界天淚下如雨，正是此事。

Śūnyatā is translated as "Emptiness"; this is the spirit presiding over space. The heavens of the formless realm are also of this category; according to what they govern, they also lack form and matter. As for "being made of wind-nature," this refers to the body being invisible, and so it says "fundamentally non-existent." By means of the Buddha's power it can temporarily manifest, which also reveals that there is matter of mastery in meditative concentration, but no matter born of karma. That the formless realm devas shed tears like rain is precisely this matter.