Day 17 covers all of Chapter 12, Devadatta, and opens Chapter 13, Encouragement for Keeping this Sutra.
At that time there were five hundred Arhats in this congregation. They had already been assured of their future attainment [of Anuttara-samyak-saṃbodhi]. They said to the Buddha, “World-Honored One! We also vow to expound this sūtra [but we will expound it] in some other worlds [rather than in this Sahā-World].”
There were also eight thousand Śrāvakas some of whom had something more to learn while others had nothing more to learn. They had already been assured of their future attainment [of Anuttara-samyak-saṃbodhi]. They rose from their seats, joined their hands together towards the Buddha and vowed:
“World-Honored One! We also will expound this sūtra in some other worlds because the people of this Sahā-World have many evils. They are arrogant. They have few merits. They are angry, defiled, ready to flatter others, and insincere.”
The fact that these Arhats and Śrāvakas refused to preach this sutra in the Sahā-World underscores the need for Encouragement for Keeping This Sutra