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

Pūrṇa, the son of Maitrāyaṇī and the preeminent preacher among the Buddha’s followers, approaches the Buddha with great joy but does not speak, does not request anything for himself. The Buddha praises Purna for strenuously protecting his teachings, and helping him propagate them. Although Purna appears to be a Śrāvaka, the Buddha explains that it is just an expedient while doing the work of the Buddha:

[Purna] 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 Śrāvaka. He benefited many hundreds of thousands of living beings with this expedient, and also caused innumerable, asaṃkhya people to aspire for Anuttara-samyak-saṃbodhi. He did the work of the Buddha, that is, taught all living beings so that the world of the Buddha might be purified.

The Arhats, on the other hand, needed reassurance from the Buddha that they, too, would one day attain Buddhahood. After they receive that assurance they reproached themselves for having satisfied themselves with the Lesser Vehicle. They tell the story of the rich man who sews a priceless gem in the garment of a poor friend. The poor man struggles for survival unaware that he has this gem.

“World-Honored One! Now we see that we are Bodhisattvas in reality, and that we are assured of our future attainment of Anuttara-samyak-saṃbodhi. Therefore, we have the greatest joy that we have ever had.”