There are two kinds of classic works on filial piety: the Classic of Filial Piety written by a non-Buddhist sage called Confucius of China and the Buddhist work on filial piety entitled the Lotus Sūtra. Although they differ in that one is a Buddhist sūtra and another is a non-Buddhist classic, what they preach is fundamentally the same.

For what purpose did Śākyamuni Buddha strive to attain Buddhahood for an incalculably long period of time known as the dust-particle kalpa (aeons)? It was for no other reason than filial piety. However, as all the living beings in the world of delusion are the Buddha’s parents, unless they all attain Buddhahood, He cannot claim to have fulfilled His filial duties. The Buddha, therefore, did not attain Buddhahood Himself. However, the Lotus Sūtra expounds the secret dharma enabling all living beings to attain Buddhahood. That is to say, it reveals the truth of attaining Buddhahood by all living beings in the ten realms through leading one person in the realm of hell, one person in the realm of hungry spirits, or just one person in each of the nine realms to Buddhahood. It is just as when we cut a bamboo joint, other joints are cut at the same time. Or it is like the shichō strategy in the game of go, where the death of one “stone” coincides with the death of many. It is the same with the truth of the Lotus Sūtra. As metal can cut trees and grass, and water has the virtue of extinguishing all fires, the Lotus Sūtra is equipped with the virtue of enabling all living beings to become Buddhas.

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