大般涅槃經義記 1.183

1.183

就明苦中，初有半偈明其麁苦，言「眾苦」者是其重苦，內有生、老、病、死等苦，外有種種逼迫等苦，名為眾苦。「無際、無息」是其深苦，過去無際、未來無息。下半明其生滅細苦。「三界無常」，明苦所以。「諸有無樂」，正明其苦。良以三界皆無常故，三有之中悉無有樂。

Regarding the explanation of suffering, first there is half a verse explaining coarse suffering; the words "manifold sufferings" are severe suffering: internally there are the sufferings of birth, old age, sickness, and death, and externally there are various sufferings of oppression and harassment, called manifold sufferings. "Boundless and unceasing" is deep suffering: past without boundary, future without cessation. The lower half explains the subtle suffering of arising and ceasing. "The three realms are impermanent" explains the reason for suffering. "The existences have no joy" directly explains their suffering. Truly because the three realms are all impermanent, within the three existences there is no joy whatsoever.