They say that it is the duty of retainers to widen the mind of the lord, and it is the duty of children to save the parents from suffering. Therefore, Venerable Maudgalyāyana saved his mother from torment in the realm of hungry spirits, and the two brothers of Princes Pure Store and Pure Eyes corrected the false view of their father, King Wonderful Adornment. Parents’ bodies as they stand become children’s bodies. Therefore, the merit of your upholding the Lotus Sūtra immediately becomes the merit of your father. Devadatta fell into the Avīci Hell but the Buddha granted him the certificate of future Buddhahood as Heavenly King Buddha. It was because Devadatta and the Buddha were members of the same clan. How much more so with you and your father. How can it be possible the merit of upholding the Lotus Sūtra by you not become the merit of the spirit of your late father?

Jōren-bō Gosho, A Letter to Jōren-bō, Writings of Nichiren Shōnin, Volume 5, Page 173