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

Last month, I focused on Purna, the son of Maitrayani. The Buddha reveals that his appearance as the Sravaka foremost in expounding the Dharma is only an expedient. He is really a Bodhisattva.

After the Buddha assures “these twelve hundred Arhats, who are present before me,” of their future attainment of Anuttara-samyak-sambodhi one after another, the arhats come to understand “we were like men of no wisdom because we were satisfied with the wisdom of the Lesser Vehicle although we had already been qualified to obtain the wisdom of the Tathagata.”

They offer the Parable of the Priceless Gem and recognize that they had forgotten that they, like Purna, are really bodhisattvas.

We thought that we had attained extinction when we attained Arhatship because we forgot that we had been taught to aspire for the knowledge of all things by you when you were a Bodhisattva just as the man who had difficulty in earning his livelihood satisfied himself with what little he had earned. You, the World-Honored One, saw that the aspiration for the knowledge of all things was still latent in our minds; therefore, you awakened us, saying, ‘Bhiksus! What you had attained was not perfect extinction. I caused you to plant the good root of Buddhahood a long time ago. [You have forgotten this; therefore,] I expounded the teaching of Nirva]Ja as an expedient. You thought that you had attained true extinction when you attained the Nirvana [which I taught you as an expedient].’

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