Day 21 covers all of Chapter 16, The Duration of the Life of the Tathāgata.
Having last month considered Śākyamuni’s 500-dust-atom lifetime, we consider Śākyamuni’s various activities during his lifetime.
“Good men! During this time I gave various names to myself, for instance, the Burning-Light Buddha. I also said, ‘That Buddha entered into Nirvāṇa.’ I did all these things only as expedients.
“Good men! When some people came to me, I saw the strength of the power of their faith and of the other faculties of theirs with the eyes of the Buddha. Then I named myself differently, and told them of the duration of my life differently, according to their capacities. l also said to them, ‘I shall enter into Nirvāṇa.’ I expounded the Wonderful Dharma with these various expedients, and caused the living beings to rejoice.
“Good men! When I saw that some people of little virtue and of much defilement were seeking the teachings of the Lesser Vehicle, I told them, ‘I renounced my family when I was young, and attained Anuttara-samyak-saṃbodhi [forty and odd years ago].’ In reality I became the Buddha in the remotest past as I previously stated. I told them this as an expedient to teach them, to lead them into the Way to Buddhahood.
This is an advantageous point to bring up Nichiren’s view that this entire chapter is specifically intended for today, this Latter Day of the Law.
QUESTION: For whom was the chapter on “The Life Span of the Buddha” expounded, revealing the Buddha’s enlightenment in the remotest past broadly and in detail?
ANSWER: “The Life Span of the Buddha” chapter together with a half chapter each preceding and following it were expounded specially for the people living after the Buddha’s extinction from beginning to end. It was expounded especially for those in this Latter Age of Degeneration such as Nichiren.
Hokke Shuyō Shō, Treatise on the Essence of the Lotus Sūtra, Writings of Nichiren Shōnin, Doctrine 2, Page 211-212