"What inspired Shakyamuni to devote himself to religious practice over kalpas equal in number to dust particles in an effort to attain Buddhahood? It was nothing other than the ideal of filial devotion. All the living beings of the six paths and the four forms of birth are our fathers and mothers. Therefore, as long as Shakyamuni was unable to treat them all with filial devotion, he refrained from becoming a Buddha. [...] Among the living beings of the six paths and the four forms of birth there are both men and women. And these men and women all were our parents at some point in our past existences. Therefore, as long as even one of these fails to attain Buddhahood, then we ourselves cannot become Buddhas."
From Gosho "Letter to Horen" (The Writings of Nichiren Daishonin Volume I, page 512)
From Gosho "Letter to Horen" (The Writings of Nichiren Daishonin Volume I, page 512)