大般涅槃經義記 9.151

9.151

上來一番當問正解，有難解者下重顯之。迦葉先問，若如佛說未來身淨可說有性，眾生現在未有淨身，何故如來說一切生皆有佛性？佛答有三：一明佛性雖無現用而體不無，故得言有。「性雖現無」無現用也，「不可言無」不無體也，「如空」喻顯。「空性無現」喻向初句，「不得言無」喻向後句。二明佛性常住不滅故得言有。「眾生無常」辨相異性，「而性常住」辨性異相。三明佛性雖復非內而復非外故得言有。於中初法、次喻、後合。

The above was one round of direct explanation in response to the question; for what is difficult to understand, it is clarified again below. Kāśyapa first asks: If, as the Buddha says, one can speak of having the nature because the future body is pure, sentient beings at present do not yet have a pure body; why then does the Tathāgata say that all sentient beings have the buddha-nature? The Buddha's answer has three parts: First, he explains that although the buddha-nature lacks present functioning, its essence is not non-existent; therefore one can say it exists. "Although the nature is presently non-existent" means it lacks present functioning; "it cannot be called non-existent" means it is not devoid of essence; "like space" clarifies it by analogy. "The nature of space lacks present [manifestation]" illustrates the first clause; "it cannot be said to be non-existent" illustrates the latter clause. Second, he explains that because the buddha-nature is permanently abiding and unperishing, one can say it exists. "Sentient beings are impermanent" distinguishes their characteristics from the nature; "yet the nature is permanently abiding" distinguishes the nature from the characteristics. Third, he explains that although the buddha-nature is neither internal nor external, one can say it exists. Within this, first is the dharma, next the analogy, and then the application.