大乘起信論裂網疏 2.81

2.81

Previously it was clarified that the ālayavijñāna has the meaning of awakening; it was also clarified that based on non-awakening one speaks of initial awakening, and awaiting initial awakening one establishes original awakening, yet initial and original are ultimately not different. Therefore, here it directly clarifies the four great meanings of the marks of awakening. Being originally free from defilement, it is called pure. Because originally no physical characteristics, directions, boundaries, or measures can be found, it is like space. Being originally tranquil and illuminating, it is like a bright mirror. For if one only spoke of being like space, there would be no way to reveal its illuminating function; if one only spoke of being like a bright mirror, there would be no way to reveal its essence and marks. Therefore, they must be combined to say "like space and a bright mirror," and only then can it somewhat serve as an analogy for the marks of awakening.