金光明最勝王經疏 2.11

2.11

問：應化行法由二因感，見可生疑。自性非因生，自受用身非餘見境，不於彼疑，何須說壽？答：自性雖非因生，然由因證。自受雖非餘見說二，欲令欣求，妙幢假化生疑，佛因具說三壽。

Question: The active phenomena of the response and transformation [bodies] are evoked by two causes, so seeing them may give rise to doubt. The essential nature (svabhāva) is not born of causes, and the self-enjoyment body is not an object seen by others; having no doubts about those, why is it necessary to speak of their life-span? Answer: Although the essential nature is not born of causes, it is nevertheless realized through causes. Although the self-enjoyment body is not seen by others, speaking of the two is intended to make beings aspire to them. Ruciraketu, through the transformation [body], gave rise to doubt, and the Buddha on that basis fully explained the three life-spans.