大乘起信論義記 3.186

3.186

"Because all dharmas... devoid of thought" cites the principle about which one is deluded. "Yet there is a deluded mind..." means that delusion arises in reliance on truth, referring to the subtle and coarse defiled minds, root and branch non-enlightenment. Intending to explain purity, it first cites its defilement to reveal it in contrast. The subsequent sentences follow the same pattern. As for how it is revealed: because the marks of the mind arising as thoughts are precisely non-enlightenment and avidyā, knowing that the mind-nature does not arise is precisely the luminous wisdom of innate enlightenment; hence it is called "the meaning of the light of great wisdom."