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

Purna, the son of Maitrayani having heard from the Buddha the Dharma expounded with expedients by the wisdom [of the Buddha] according to the capacilies of all living beings, and having heard that [the Buddha] had assured the great disciples of their future attainment of Anuttara-samyak-sarnbodhi, and also having heard of the previous life of the Buddha, and also having heard of the great, unhindered, supernatural powers of the Buddhas, had the greatest joy that he had ever had, became pure in heart, and felt like dancing [with joy].

And so begins Chapter 8. The Buddha praises Purna as “the most excellent expounder of the Dharma.”

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.

The Buddha reminds us that Purna appears to be a Sravaka only as an expedient for spreading the Dharma:

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.

And in gathas:

Bhisksus, listen to me attentively!
The Way practiced by my sons
Is beyond your comprehension
Because they learned how to employ expedients.

Knowing that people wish to hear
The teachings of the Lesser Vehicle,
And that they are afraid of having the great wisdom,
[My sons, that is,] the Bodhisattvas transform themselves
Into Sravakas or cause-knowers,
And teach the people with innumerable expedients.

Saying to the innumerable living beings, [for instance,]
“We are Sravakas.
We are far from the enlightenment of the Buddha,”
They save them, and cause them to attain [Sravakahoodl
Even the lazy people who wish to hear the Lesser Vehicle
Will become Buddhas with this expedient in the course of time.

My disciples are performing
The Bodhisattva practices secretly
Though they show themselves in the form of Sravakas.
They are purifying my world
Though they pretend to want little
And to shun birth-and-death.
In the presence of the people,
They pretend to have the three poisons and wrong views.
They save them with these expedients.
They change themselves into various forms.
If I speak of all their transformations,
The listeners will doubt me.

The 1,200 Arhats, having heard of the future Buddhahood of Purna and the others, seek assurance of their opportunity and the Buddha complies, saying, “Now I will assure these twelve hundred Arhats, who are present before me, of their future attainment of Anuttara-samyak-sambodhi one after another.” And if anyone feels left out he adds:

All the other Sravakas also will [become Buddhas].
Tell this to the Sravakas
Who are not present here!

The Arhats, who feel like dancing at the news, offer the Parable of the Priceless Gem to explain why they settled for the Lesser Vehicle.

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.”

And in gathas:

We are like the poor man.
In the long night you taught us
Out of your compassion towards us,
And caused us to aspire for unsurpassed [enlightenment].

Because we had no wisdom, we did not notice that
The Nirvana we attained was only part [of your wisdom].
Satsifying ourselves with it,
We did not wish to attain anything more.

Now you have awakened us, saying:
“What you attained was not true extinction.
When you have the unsurpassed wisdom of the Buddha,
You will attain true extinction.”

Hearing from you that we are assured
Of becoming Buddhas one after another,
And that our worlds will be adorned,
We are joyful in body and mind.