大般涅槃經疏 12.30

12.30

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.