大般涅槃經義記 5.49

5.49

Second, distinguishing in terms of conditions and essence: the nature of mind is suffering, and adding suffering upon suffering is therefore called the "suffering of suffering." What kind of suffering is added? Namely, adding the former three sufferings with respect to conditions, all together called the suffering of suffering. Conditioned dharmas will inevitably decay and be destroyed, which is called the "suffering of change." The constant flux of these very conditioned phenomena is called activity, and the nature of activity being uneasy is called the "suffering of conditioned existence."