Nichiren Daishonin states in “On the Heritage of the Ultimate Law of Life and Death”:
All disciples and believers of Nichiren should chant Nam-Myoho-Renge-Kyo with the spirit of many in body, one in mind, overcoming all differences among themselves, [to become united with the heart of the Buddha], just like fish being inseparable from the water in which they swim. This is called the heritage of the ultimate Law of life and death. This is also what Nichiren is trying to propagate now in the Latter Day of the Law. When you are so united, even the great aspiration for kosen-rufu can be fulfilled without fail. However, if there are any among Nichiren’s disciples who are many in body, many in mind, they are like subjects in a castle who destroy the fortress from within.