Day 17 covers all of Chapter 12, Devadatta, and opens Chapter 13, Encouragement for Keeping this Sutra.
Having last month learned who the seer who taught the king was, we hear the prediction for Devadatta’s future and the future of those who receive this chapter.
He said to the four kinds of devotees:
“Devadatta will become a Buddha after innumerable kalpas.’ He will be called Heavenly-King, the Tathāgata, the Deserver of Offerings, the Perfectly Enlightened One, the Man of Wisdom and Practice, the Well-Gone, the Knower of the World, the Unsurpassed Man, the Controller of Men, the Teacher of Gods and Men, the Buddha, the World-Honored One. The world of that Buddha will be called Heavenly-Way. That Buddha will live for twenty intermediate ka]pas. He will expound the Wonderful Dharma to all living beings. [Hearing the Dharma from him,] as many living beings as there are sands in the River Ganges will obtain Arhatship; another group of innumerable living beings will aspire for the enlightenment of cause-knowers; and another group of living beings as many as there are sands in the River Ganges will aspire for unsurpassed enlightenment, obtain the truth of birthlessness, and reach the stage of irrevocability. After the Parinirvana of Heavenly-King Buddha, his right teachings will be preserved in that world for twenty intermediate kalpas. During that time a stupa of the seven treasures sixty yojanas tall and forty yojanas wide and deep will be erected to enshrine the śarīras of his perfect body. Gods and men will bow to the wonderful stupa of the seven treasures and offer various flowers, incense powder, incense to burn, incense applicable to the skin, garments, necklaces, banners, streamers, jeweled canopies, music and songs of praise [to the stupa]. [By doing all this,] innumerable living beings will attain Arhatship; another group of innumerable living beings will attain Pratyekabuddhahood; and another group of inconceivably numerous living beings will aspire for Bodhi and reach the stage of irrevocability.”
He said to the bhikṣus:
“Good men or women in the future who hear this chapter of Devadatta of the Sūtra of the Lotus Flower of the Wonderful Dharma with faithful respect caused by their pure minds, and have no doubts [about this chapter], will not fall into hell or the region of hungry spirits or the region of animals. They will be reborn before the Buddhas of the worlds of the ten quarters. They will always hear this sūtra at the places of their rebirth. Even when they are reborn among men or gods, they will be given wonderful pleasures. When they are reborn before the Buddhas, they will appear in lotus-flowers.”
Nichiren offers this explanation of why Devadatta’s sins did not preclude his becoming a Buddha in the Lotus Sūtra:
[R]egarding the three rebellious sins committed by Devadatta, although he caused the Buddha to bleed, this Buddha was the Buddha before the Lotus Sūtra was preached and not the Original and True Buddha who attained Enlightenment in the eternal past. He also killed an arhat, but this arhat was the one before the Lotus Sūtra was preached, not the practicer of this sūtra. He disrupted the harmony in a Buddhist order, but it was not the order based on the great sudden and perfect Lotus precepts, but on the Hinayana precepts before the Lotus Sūtra was preached. As a result, although the earth split open and Devadatta fell into the Hell of Incessant Suffering, because he had not actually committed the three rebellious sins against the Lotus Sūtra, he could therefore still become the Heavenly King Buddha in the Lotus Sūtra.
Ha Ryōkan-tō Gosho, A Letter Refuting Ryōkan-bō and Others, Writings of Nichiren Shōnin, Volume 5, Pages 55-56