大乘起信論廣釋卷第三．四．五 3.75

3.75

[Treatise:] Why is this? [...] only a Buddha can know. [Commentary:] This explains the meaning of why it is profound. The subtle principle of dependent origination runs through ordinary persons and sages, yet only a Buddha exhaustively understands it. Why is this? In the answer text below there are three sections. First, clarifying that while pure, it is constantly defiled: "This mind's original self-nature is pure" means that the true mind of dependent origination, which is original awakening, speaking in terms of its origin, is in its own substance undefiled; it is not that there is another pure dharma that could make it pure; this generally reveals the cause of dependent origination. "Yet there is avidyā" means that relying on the mental substance there is this condition of avidyā and non-awakening; this reveals the condition of dependent origination. "Being defiled by avidyā, there is a defiled mind" means that the mental substance is defiled by this avidyā, and on the pure mental substance there is a defiled mind; this reveals the characteristic of dependent origination. All this explains the sūtra's "undefiled yet defiled." "Revealing that there is a defiled mind," etc.: Next, clarifying that while defiled, it is constantly pure. It means that although the mind of original awakening is defiled by it, constantly having a defiled mind, its nature is inherently real, so it does not lose its fundamentally pure mental nature. This explains the sūtra's "defiled yet undefiled." "Only a Buddha can exhaustively understand" clarifies that the Buddha can know this: since this principle is so profound, it is not fully understood by others, hence the principle of dependent origination can only be known by a Buddha. Thus the Śrīmālā [Sūtra] says: "The intrinsically pure mind is difficult to understand; that that mind is defiled by afflictions is also difficult to understand." The Laṅkāvatāra Sūtra says: "The tathāgatagarbha has a pure mark, yet is defiled and impure with the stains of adventitious defilements. Now I, together with you and the bodhisattvas of profound wisdom, are able to fully understand and distinguish it." The present treatise comments on this to show its profound depth.