Nichiren’s writings say very little about the place of his mandala (or of Buddha images) in actual practice. There is one personal letter, the “Nichinyo gozen gohenji,” which does touch on this issue, and though some modern scholars dispute its authenticity, it has historically been highly valued in the Nichiren tradition for its easily accessible description of the mandala and its relation to the practitioner’s faith:

Never seek this gohonzon elsewhere, [for] it abides only in the fleshly heart within the breast of persons like ourselves who embrace the Lotus Sūtra and chant Namu-myōhō-renge-kyō. This is called the capital city of suchness, the ninth consciousness that is the mind-ruler (kushiki shinnō shinnyo no miyako). Being endowed with the ten realms means that [all] ten realms, not excepting a single one, are contained within a single realm, [that of Buddhahood]. That is the reason why this is called a mandala. “Mandala” is a word from India. Here [in Japan] it is called “perfect endowment” (Tinnen gusoku) or “cluster of merits” (kudokuju). This gohonzon is contained solely within the word “faith.” That is the meaning of “gaining entrance by faith.” By believing undividedly in [the Lotus Sūtra, in accordance with its words,]” honestly discarding skillful means” and “not accept[ing] even a single verse from other sūtras, ” Nichiren’s disciples and lay followers shall enter the jeweled stūpa of this gohonzon. How reassuring, how reassuring!

If one judges by this passage, it appears that the logic of Nichiren’s mandala is quite similar to that of esoteric practice, wherein the practitioner visualizes the union of self and Buddha, known as “the Buddha entering the self and the self entering the Buddha” (nyūga ganyū). For Nichiren, however, the nonduality of the practitioner and the Buddha is realized neither by esoteric visualization techniques nor by introspective contemplation involving the application of mental categories, such as the threefold contemplation. Rather, it is by faith in the Lotus Sūtra that one enters the realm of the Buddha’s enlightenment–the three thousand realms in a single thought-moment as actuality–and manifests its identity with oneself. (Page 280-288)