大般涅槃經義記 2.131

2.131

〈金剛身品〉者，此品之中具答二問：一答云何得金剛身、二答何因得堅固力。此二因同，一處答之。於此二中就始以標，是故名為〈金剛身品〉。下文之中具辯五身，何故偏名〈金剛身品〉？不可並題，且舉金剛就第一問，偏云金剛。此品有四：一明得身、二總結嘆、三迦葉領解、四如來述讚。就初段中，先明其果，而未能知所因已下辯其得因。向前品中先因後果，今乘前便，先果後因。就明果中，先略、後廣。「如來身者是常住身乃至法身」，是其略也，身體不遷名常住身，不為緣沮名不壞身。不壞之義如世金剛，是故就喻名金剛身。不假資成名「非雜食身」，唯以法成名為「法身」。

As for the "Chapter on the Diamond Body," in this chapter two questions are answered in full: first, answering how one attains a diamond body; second, answering by what cause one attains firm strength. Because the causes for these two are identical, they are answered in a single place. Between these two, it is labeled according to the beginning, and is therefore named the "Chapter on the Diamond Body." In the text below, five bodies are distinguished in full; why is it exclusively named the "Chapter on the Diamond Body"? They cannot be titled together, so for now it adduces the diamond in reliance on the first question, exclusively calling it diamond. This chapter has four parts: first, explaining the attainment of the body; second, summarizing and praising; third, Kāśyapa comprehends; fourth, the Tathāgata narrates and praises. In the first section, he first clarifies the fruit, and from "yet has not been able to know that from which it is caused" onwards he distinguishes the cause of its attainment. In the preceding chapter, first was the cause and afterwards the fruit; now, taking advantage of the preceding flow, first is the fruit and afterwards the cause. In clarifying the fruit, first is brief, and afterwards broad: "The Tathāgata's body is a constantly abiding body, up to a dharmakāya" is the brief. The bodily essence not changing is called the constantly abiding body; not being broken by conditions is called the indestructible body. The meaning of indestructibility is like worldly diamond, and is therefore named the diamond body according to analogy. Not relying on nourishment to be accomplished is called the "non-miscellaneous-food body"; being accomplished solely through Dharma is called the "dharmakāya."