大般涅槃經義記 1.187

1.187

第二段中，「究竟斷有」，明其除苦。「今當涅槃」，明其得滅。實自久證，對今息化，始歸其實，故言今日當涅槃矣。

In the second section, "ultimately severing becoming" explains the removal of suffering. "I shall now enter nirvāṇa" explains the attainment of extinction. In truth, [the Buddha] had long realized it; but relative to the cessation of his transformation now, he only now returns to the real; hence it says that today he will enter nirvāṇa.