Prince Shōtoku of Japan was a son of Emperor Yōmei, the thirty-second sovereign of Japan. When he was six years old, elderly men coming from Paekche, Koguryō, and T’ang China paid homage to the Emperor. The six-year old crown prince declared that they were his disciples, and these elderly men holding hands in reverence said that the crown prince was their teacher. It was indeed a wonder. It is also said in a non-Buddhist work that a certain man, while walking on a street, came across a young man about thirty years old beating an old man of about eighty years old on the street. Asked what was the matter, the story says, the young man answered that this elderly man he was beating was his son. The relationship between Śākyamuni and great bodhisattvas from underground is similar to these stories.

Therefore, Bodhisattva Maitreya and others asked a question, “World Honored One! When You were the crown prince, You left the palace of the Śākya clan and sat in meditation under the bodhi tree not far from the town of Gayā until You attained perfect enlightenment. It has only been forty years or so. How could You, World Honored One, achieve so much in so short a time?”

For forty years or so starting with the Flower Garland Sūtra, bodhisattvas have asked questions in every assembly to dispel the doubts all beings might have had. This, however, is the most serious question of all. In the Sūtra of Infinite Meaning, for instance, 80,000 bodhisattvas such as Great Adornment put forth a serious question concerning the apparent discrepancy in time required for attaining Buddhahood. While it has been said in the sūtras preached in the first forty years or so that it would take many kalpa, now it was preached that one could obtain Buddhahood quickly through the teaching of the Sūtra of Infinite Meaning. However serious the question of Great Adornment Bodhisattva was, that of Maitreya was more crucial. …

The thirty-six questions asked by Kāśyapa in the Nirvana Sūtra were also not as serious as the one asked by Maitreya. If the Buddha had not squarely answered the question to dispel this doubt, all the holy teachings of the Buddha’s lifetime would have appeared to be as worthless as bubbles, and the questions of everyone would have remained unanswered. Here lies the importance of the sixteenth chapter, “The Life Span of the Buddha,” of the Lotus Sūtra.

Kaimoku-shō, Open Your Eyes to the Lotus Teaching, Writings of Nichiren Shōnin, Doctrine 2, Page 72-74