大般涅槃經疏 12.30

12.30

「迦葉白佛何緣」下，是品中第十，答上云何為生盲而作眼目導。先騰脣口乾焦，即生盲義。佛答中，先答口爽、次答生盲。初云口爽者，不知三寶常住之味，名為口爽。口爽即是生盲，若計定有，撿覓即無。從「復次善男子」下，答生盲。盲故即是不識。不識手足者，不識身內之佛性也。

From "Kāśyapa addressed the Buddha: For what reason" onwards is the tenth [section] within the chapter, answering the preceding [question], "How does he serve as eyes and guide for those blind from birth?"
First, bringing up "lips and mouth parched and burnt" refers to the meaning of being blind from birth.
In the Buddha's answer, he first answers "the mouth losing its sense of taste," and next answers "blind from birth."
First, saying "the mouth losing its sense of taste" means not knowing the flavor of the eternal abiding of the Three Jewels, which is called the mouth losing its sense of taste. The mouth losing its sense of taste is itself being blind from birth; if one grasps it as definitely existent, when examined and sought, it is non-existent.
From "Furthermore, good son" onwards, he answers "blind from birth." Because of being blind, one does not recognize. Not recognizing hands and feet means not recognizing the buddhadhātu within one's own body.