This happened before the parallel mode of expression, "Kongokai (Diamond Realm) or Taizokai (Womb Realm)," became remarkable after Kakuban Kokyo Daishi in the latter Heian period, and should be understood as an epoch, regarding the religious beliefs particular to the Japanese, in conducting and discussing each master's standpoint or background related with Nini-Funi (also known as Funi-Nini (two sides of the same coin)) in which Oei no Taisei (Perfection in Oei era) reached the summit, more over in the Japanese intellectual history of Esoteric Buddhism, especially practicing or considering Jikyo niso (Jiso (method to practice the doctrine) and Kyoso (logical study of doctrines)).
これは平安後期の覚鑁興教大師以降、『金剛界／胎蔵界』という並立的表現方法が顕著となる以前の出来事であり、日本固有の信仰観について、後の応永の大成を頂点とする二而不二／不二而二に係わる各法匠の立場／背景、さらには日本の密教思想史、殊に事教二相を実践／検討する上で銘記するべき事象として理解することを求められよう。