To accept the theory that the realm of Buddha exists and that Śākyamuni Buddha exists in oneself are quite different in meaning. Here the world of “Ri” changes to the world of “Ji” and the theoretical and philosophical doctrine becomes the warm hearted religious doctrine. Nichiren Shōnin said,

“Śākyamuni Buddha within our minds,” (Kanjin Honan
Shō, WNS2, page 146)

and,

“the World Honored One is in my (Nichiren’s) head” (Oto Gozen Goshōsoku).

Ichinen Sanzen of Ji and the Essential Section are based on these words.