金光明最勝王經疏 2.13

2.13

Question: When the four Buddhas spoke of the life-span, Ruciraketu gave rise to understanding; why was it necessary for Śākyamuni to repeat the explanation? Answer: Bodhi and nirvāṇa are the unexcelled, marvelous fruits; if they are not explained three times, others cannot understand them. Therefore, the four Buddhas first proclaimed it, Śākyamuni repeated it, Kaundinya questioned it again, and Priyadarśana further made it clear. The four Buddhas manifested the four virtues, and the three explanations stood for the three bodies; on account of these many reasons, it was not spoken only once.