Nichiren Daishonin states in “Reply to Nichinyo gozen”:
This Gohonzon exists within faith alone, as expressed by the two characters, “belief” and “heart” (shin-jin). This is what is meant by “gaining entrance [to enlightenment] through faith alone” [in the Lotus Sutra]. The disciples and followers of Nichiren, without any doubt, wholeheartedly believe in “honestly discarding expedient means” and “not accepting a single verse of the other sutras.” Thus, they can enter the Treasure Tower of the Gohonzon. How encouraging, how heartening! By all means, exert your best efforts for the sake of your future lives. It is most important to chant only Nam-Myoho- Renge-Kyo and attain Buddhahood. This will depend on the strength of your faith. The essence of Buddhism is to have faith.
此御本尊亦只纳于信心二字。以信得入者是也。日莲之弟子檀那等，以“正直舍方 便”、“不受余经一偈”，无二信之故，得入此御本尊之宝塔中也。幸甚幸甚。无论如何后生必安稳，必安稳。诚惶诚恐。唯唱南无妙法莲华经而成佛之事尤为重 要。应依信心之厚薄也。佛法之根本以信为源。