One’s life span is one’s prime treasure. Extending it even by one day is worth more than ten million ryō of gold coins. The reason why the Lotus Sūtra is the most superior of all the scriptures of Buddhism is due to the eternal life span of the Buddha expounded in its “Life Span of the Buddha” chapter. Even the crown prince of the world’s greatest empire is worth less than a weed if he dies young. Even a wise person as shiny as the sun is not worthy of a dog if he dies while still young.
Kaen Jōgō Gosho, Writing About Lengthening the Life Span, Writings of Nichiren Shōnin, Volume 7, Followers II, Pages 114