Day 13 covers all of Chapter 8, The Assurance of Future Buddhahood of the Five Hundred Disciples.

Last month covered the opening of the chapter with Purna expressing his appreciation for what he has just learned. Now we hear from the Buddha the importance of Purna and his hidden role:

Thereupon the Buddha said to the bhiksus:

Do you see this Purna, the son of Maitrayana? I always praise him, saying that he is the most excellent expounder of the Dharma. I also praise him for his various merits. He strenuously protects my teachings, and helps me propagate them. He shows the Way to the four kinds of devotees, teaches them, benefits them and causes them to rejoice. He explains my right teachings perfectly, and gives great benefits to those who are performing brahma practices with him. No one except the Tathagata excels him in eloquence. Do not say that he protects only my teachings and helps me propagate them! In his previous existence he also protected the right teachings of nine thousand million Buddhas and helped them propagate their teachings. Under those Buddhas also he was the most excellent expounder of the Dharma. He clearly understood the truth of the Void expounded by those Buddhas, and obtained the four kinds of unhindered eloquence. He always expounded the Dharma clearly and purely, with no doubtfulness. Although he had the supernatural powers of Bodhisattvas, he performed brahma practices throughout his previous existence. Therefore, the people of the world of the Buddha [under whom he performed brahma practices] thought that he was a Sravaka. He benefited many hundreds of thousands of living beings with this expedient, and also caused innumerable, asamkhya people to aspire for Anuttara-samyak-sambodhi. He did the work of the Buddha, that is, taught all living beings so that the world of the Buddha might be purified.

Underline the people of the world of the Buddha [under whom he performed brahma practices] thought that he was a Sravaka. As Sakyamuni makes clear in the gathas, Purna is really a bodhisattva who only appears to be a Sravaka as an expedient necessary to teach the Dharma.