大般涅槃經集解 2.21

2.21

案僧亮曰：下文有釋。彼土唯立三時，謂春夏冬也。二月是春和之中節，異耶。冬夏寒暑，偏也明也。昔說苦空，如彼之偏；今既二理雙顯，故取表於中和也。僧宗曰：此是榮枯交代之節。將明如來二種法身，捨迹歸本者也。智秀曰：臨涅槃時者，指說經之時也。

I note that Sengliang says: "The text below has an explanation. That land only establishes three seasons, namely spring, summer, and winter. The second month is the harmonious mid-season of spring; is it not distinct? Winter and summer, cold and heat, are partial and clear. Formerly, the teachings on suffering and emptiness were partial like that; now, since the two principles are doubly manifested, [this month] is chosen to symbolize harmony and the middle." Sengzong says: "This is the season when flourishing and withering alternate. It is intended to clarify the Tathāgata's two kinds of dharmakāya, abandoning the traces to return to the root." Zhixiu says: "'When he was about to enter nirvāṇa' refers to the time of preaching the sūtra."