大乘起信論義記 3.239

3.239

In the specific explanation, 'from the beginning form and mind have been non-dual' means that the forms of the reward and transformation [bodies] manifested therein are not different from the true mind of the dharmakāya, just as waves and water have originally been non-dual. The statement from 'because the nature of form is precisely cognition' and so forth clarifies that form is precisely mind, revealing the preceding non-duality. Because form is precisely mind, it immediately causes marks of form to be completely exhausted; therefore, in terms of its origin, it merely speaks of the 'cognition-body.' 'Cognition' refers to the mind-cognition of innate enlightenment. The statement 'because the nature of cognition is precisely form, the dharmakāya is said to pervade all places' clarifies that mind is precisely form, revealing the preceding non-duality, just as water is everywhere within the waves.