Even if one believes in the pre-Lotus sūtras, if one does not believe in the Lotus Sūtra and chant Namu Myōhō Renge-kyō even once, one is an undutiful child. He will be abandoned by the Buddhas and bodhisattvas in all the worlds throughout the universe in the past, present and future, and also will be begrudged by the gods of heaven and earth.

Nanjō Hyōe Shichirō-dono Gosho, A Letter to Lord Nanjō Hyōe Shichirō, Writings of Nichiren Shōnin, Doctrine 3, Pages 140.