大乘起信論義記 3.192

3.192

非常等者，明妄四失；返之即顯真如四德。諸惑燒心，是極熱惱，故說真如是清涼也。妄染遷改，是衰變相，即返顯真如為不變。以業果繫縛不自在故，即顯真如為自在也。故上文云「清涼不變自在義故」也。

"Non-permanent..." clarifies the four faults of delusion; reversing this reveals the four virtues of tathatā. The afflictions burning the mind are extreme heat and anguish; hence it is said that tathatā is coolness. Deluded defilement shifting and altering is the mark of decay and change; this inversely reveals that tathatā is unchanging. Because it is bound by karmic fruit and not sovereign, this inversely reveals that tathatā is sovereign. Hence the previous text said: "Because of the meanings of coolness, unchangingness, and sovereignty."