Men and women comprise the living beings who exist in the world of delusion. They were all our parents at some point in our previous lives. Therefore, if there is even a single person who cannot become a Buddha, we, too, are unable to become Buddhas. It is preached that the Two Vehicles do not appreciate the favors they received, and therefore they are forever unable to attain Buddhahood. In short, it is because they are full of ego and unable to treat all living beings with a heart of filial piety. Convinced of the Lotus Sūtra, the Buddha considers all the people in the world of delusion as His parents and He is equipped with the virtue of filial piety.

Śākyamuni Buddha then turns over this virtue of filial piety to those who embrace the Lotus Sūtra. It is like the food taken by a mother that is transformed into breast milk to feed her baby. As it is preached in the “Parable” chapter of the Lotus Sūtra: “Now this triple world is all My domain, and all the living beings in it are all My children,” our Lord Preacher Śākyamuni Buddha feeds us all the living beings in this world of delusion with His virtue of filial piety transformed into the characters of the Lotus Sūtra. It is like a baby, who does not distinguish water from fire or poison from medicine, who can sustain its life by swallowing its mother’s milk.

Hōren-shō, Letter to Hōren, Writings of Nichiren Shōnin, Volume 6, Followers I, Page 51-52