大般涅槃經義記 7.115

7.115

自下第三答上後段不定之難，論其答辭，述前所問，明佛不定。語其答意備有三義：一明如來體不定故，雖現世間而常不同，以不同故常、樂、我、淨；二明如來體不定故，雖得涅槃，不捨世間，常隨諸有，常隨有故，不畢竟滅；三明如來不決定故，在有恒常，以其常故，一闡提等當必得之，以當得故現有佛性。

From here below is the third part, answering the challenge regarding indeterminacy in the latter section above. As for the phrasing of the answer, it affirms what was asked previously, explaining that the Buddha is indeterminate. Speaking of the intention of the answer, it possesses three meanings: First, clarifying that because the Tathāgata's essence is indeterminate, although manifesting in the world, it is ever dissimilar; because it is dissimilar, it is permanent, blissful, self, and pure. Second, clarifying that because the Tathāgata's essence is indeterminate, although attaining nirvāṇa, he does not abandon the world, ever following all realms of existence; because he ever follows existence, he does not undergo ultimate extinction. Third, clarifying that because the Tathāgata is not determinate, he is eternal amidst existence; because he is eternal, icchantikas and the like will definitely attain him in the future; because they will attain him in the future, they currently possess the buddha-nature.