大般涅槃經義記 1.15

1.15

問曰：諸人多以三分科判此經，今以何故離分為五？釋言：准依《勝鬘經》等三分科文，實有道理，故彼經中十五章前別有由序，十五章後別立流通。此經判文不得同彼，以第五分非流通故。又諸論者作論解經，多亦不以三分科文。五中，初一化益方便、中三正益、後之一分化訖取滅。

Question: Most people divide this sūtra into three sections; why is it now divided into five? Explanation: Following the threefold division of texts as in the Śrīmālādevī Sūtra is indeed reasonable, for in that sūtra there is a distinct origin and preface before the fifteen chapters, and a distinct dissemination section established after the fifteen chapters. The division of the text of this sūtra cannot be the same as that, because the fifth section is not a dissemination section. Moreover, when treatise masters compose treatises to explain sūtras, they also mostly do not divide the texts into three sections. Among the five, the first is the expedient means for transforming and benefiting; the middle three are the principal benefit; the final section is the completion of transformation and the entry into extinction.