大乘起信論義記 2.17

2.17

Question: Since the two gates equally subsume each other, why is it that in the text above, the gate of tathatā only reveals the essence of the Mahāyāna and does not display the marks and function, whereas the gate of arising and ceasing fully displays the three? Answer: Tathatā is the gate of eliminating marks and revealing the real; without destroying marks it immediately eliminates them, and hence can subsume arising and ceasing; because it eliminates marks so that they do not remain, it only reveals the essence. Arising and ceasing is the gate of gathering the principle to form phenomena; without destroying the principle it forms phenomena, and hence can subsume tathatā; because phenomena are formed without losing the principle, it fully reveals the three greatnesses.