大般涅槃經義記 7.71

7.71

問曰：何不望直正答在先類乎？釋言：如來兼欲使人解知向前到、不到義，故先類之。於中初先開列四門，四中前二對彼涅槃不到之法，明凡未到、聖人已到；後二約對生死惡法，明聖不到、凡夫人到。

Question: Why does [the Buddha] not reply directly to the main question first, instead of drawing analogies? Explanation: The Tathāgata simultaneously wished to lead people to understand the meaning of the preceding "reaching and not reaching"; therefore he first drew an analogy to it. Therein, he first set forth four approaches. Among the four, the first two concern the dharma of nirvāṇa which cannot be reached, explaining that ordinary beings have not yet reached it while noble ones have already reached it; the latter two concern the evil dharmas of saṃsāra, explaining that noble ones do not reach them while ordinary beings do reach them.