The secret dharma (five characters of Myō, Hō, Ren, Ge, and Kyō), the essence of the Lotus Sūtra, that such great sages as Kāśyapa, Ānanda, Nāgārjuna and Vasubandhu of the Age of the True Dharma and Grand Masters T’ien-t’ai and Dengyō of the Age of the Semblance Dharma knew in mind but did not yet propagate outwardly, is clearly stated in the Lotus Sūtra. It is also clear, however, that this secret dharma is not explained at all in any commentary or annotation. Sages with an inborn capacity of perception should know the dharma by looking at the sūtra themselves. Wise persons should meet virtuous teachers, receive the dharma and believe it. Those with serious sins will distrust and hold in contempt such teachers and will not believe the dharma, but if they wish to listen to it even for a moment, I am willing to tell you about it.

Soya Nyūdō-dono-gari Gosho, A Letter to Lay Priest Lord Soya, Writings of Nichiren Shōnin, Doctrine 3, Pages 169.