大乘起信論義記 2.103

2.103

In the first part, "free from thoughts" means being free from deluded thoughts, revealing that there is no non-enlightenment. "Equal to empty space" and so forth: not only is there no darkness of non-enlightenment, but it also possesses the meaning of the great radiant light of wisdom and so forth. Empty space has two meanings by which it illustrates innate enlightenment: first, the meaning of all-pervasiveness, meaning that horizontally it pervades the three time periods, and vertically it extends through ordinary people and sages; therefore it says "pervading everywhere". Second, the meaning of being without distinction, meaning that within entanglement and when freed from hindrances, its nature is constantly non-dual; therefore it says "the single mark of the dharmadhātu". Desiring to illuminate the meaning of enlightenment, the mark of emerging from entanglement is revealed; therefore it says "is precisely the equal dharmakāya of the Tathāgata". Since it is the enlightenment of the dharmakāya, in principle it is not newly accomplished; therefore it says "relying on this dharmakāya, it is spoken of as innate enlightenment". As the commentary on the Mahāyānasaṃgraha by Asvabhāva says: "Stainless and unimpeded cognition is named the dharmakāya." The Suvarṇaprabhāsasūtra names the great round mirror cognition as the dharmakāya, and so on; all have this meaning.