大般涅槃經義記 2.79

2.79

問曰：前說施食故得，今以何故重問其因？釋言：壽命有二種因：一者養因，所謂施食，如世養母；二者生因，所謂慈悲不殺等行，如世生母。前說施食，其因未圓，故復問之，餘皆同爾。

Question: It was previously said that it is attained through giving food; why now does he ask about its cause again? Explanation: Life span has two kinds of causes: first, the nourishing cause, namely giving food, like an adoptive mother in the worldly realm; second, the generating cause, namely practices such as compassion and non-killing, like a birth mother in the worldly realm. What was said previously regarding giving food was not yet complete in its cause, and therefore he asks about it again; the rest are all like this.