大乘起信論義記 2.26

2.26

In the first part, "one dharmadhātu" means that the non-dual true mind is the one dharmadhātu. This is not the "one" of counting; because the principle is empty and fused, equal and non-dual, it is called "one." Moreover, in contrast to having two meanings below based on words, here, in terms of essence, it simply says "one." Because noble dharmas are produced in reliance [upon it], it is called "dharmadhātu." The Madhyāntavibhāgaśāstra says: "'Dharmadhātu' means that because the cause of noble dharmas is its meaning, it is therefore called dharmadhātu; noble dharmas are produced relying on this realm, and here the meaning of cause is the meaning of dhātu." Regarding "great universal mark": between the two gates, it does not take the gate of particular marks; within them it takes only the universal mark, yet it also comprehensively gathers all particulars; hence it is called "great." This one dharmadhātu in its entirety acts as the gate of arising and ceasing, and in its entirety acts as the gate of tathatā; to reveal this meaning, it says "essence." That which provides a standard to generate understanding in beings is called "Dharma"; that through which noble cognition freely traverses is called "gate."