大乘起信論義記 1.127

1.127

前中責有二意：一云、心通染淨，大乘唯淨，如何此心能顯大乘之義？又云：心法是一，大乘義廣，如何此心能示於義？釋意云：大乘雖淨相，用必對染成故。今生滅門中，既具含染淨，故能顯也，以廢染之時則無淨用故。此釋初意也。又心法雖一，而有二門，真如門中示大乘體，生滅門中具宗三大，大乘之義莫過是三，是故依此一心得顯三大之義也。立別門中，言是心真如者，總舉真如門，起下文中「即是一法界」已下文也。言相者，即是真如相，起下「復次，真如者依言說分別」已下文也。

In the former, the challenge has two senses. The first says: The mind extends to both defilement and purity, whereas Mahāyāna is solely pure; how can this mind reveal the meaning of the Mahāyāna? The second says: The dharma of the mind is one, whereas the meaning of the Mahāyāna is vast; how can this mind show this meaning? The explanation says: Although Mahāyāna is pure in its characteristics, its function must be accomplished in relation to defilement. Now, since the gate of arising and ceasing fully contains both defilement and purity, it is capable of revealing it, because when defilement is abolished, there is no pure function. This explains the first sense. Furthermore, although the dharma of the mind is one, there are two gates: within the gate of tathatā the substance of the Mahāyāna is shown, and within the gate of arising and ceasing the three greatnesses are fully grounded; the meaning of the Mahāyāna does not exceed these three. Therefore, relying on this One Mind, the meaning of the three greatnesses can be revealed. In establishing the specific gates, "this mind as tathatā" generally adduces the gate of tathatā, initiating the text below from "namely, the one dharmadhātu" onward. "Mark" is precisely the mark of tathatā, initiating the text below from "Furthermore, tathatā, when differentiated according to verbal explanation..." onward.