大乘起信論義記 3.214

3.214

Question: Why is the Buddha's body solely the consciousness of sentient beings? Answer: The true mind of sentient beings and the substance of all Buddhas are equal and non-dual; but sentient beings are deluded about their own true principle and give rise to deluded thoughts, at which time tathatā merely manifests defiled marks and does not display its function. Because that innate enlightenment internally perfumes the deluded mind, there is aversion and aspiration; because there is aversion and aspiration, the true function immediately manifests. Because aversion and aspiration are inferior, the marks of function are coarse; as aversion and aspiration gradually increase, the function also gradually becomes subtle. In this way, gradually reaching the source of the mind, once avidyā is exhausted and aversion and aspiration entirely cease, incipient enlightenment is identical to the innate, and function returns to the substance, equal and uniform, non-dual and non-different. Before reaching the source of the mind, the function manifests in consciousness according to the capacities [of beings]; hence it is said to manifest in consciousness.