首楞嚴義疏注經 9.78

9.78

'Completely investigating' means exhausting to the utmost. 'All subtle beginnings' are the subtle beginnings of all existents, namely passing from nonexistence into existence at the point where the principle of form has not yet taken shape. Now this single heaven exhausts to the point where the principle of form has not yet taken shape; hence it is said, 'completely investigating all subtle beginnings.' 'Exhausting the nature of the nature of form': 'nature' is the essence; pushing to the primal essence of the nature of form. Regarding the meaning of the two clauses, there are many precedents earlier; or, the former clause exhausts consciousness conditioned by form and the like, while the latter clause exhausts the great elements on which it relies. Bordering this heaven, one immediately enters the sphere of space, so it is said, 'entering the boundary of the limitless.' Because space is in turn that upon which the great elements rely, it is called the Utmost of Form (Akaniṣṭha). As Aśvajit asked the Buddha: 'In what stage are the natures of the four great elements completely extinguished without remainder?' The Buddha said: 'The preparatory stage of the sphere of space, which is precisely this heaven.'