Around the end of the 8th century, Japanese gods were considered as one with Buddha, and the Honji-suijaku theory was born, which claims that the true form of Buddha, appeared temporarily in form of a god to save the people of Japan, and this later became the foundation for the idea of synchronizing Shinto and Buddhism.
やがて8世紀末ごろから、日本の神々は仏と同体と考えられ、本地である仏が日本の人々を救済するために仮に神に姿をかえてあらわれたとする本地垂迹（ほんじすいじゃく）説が発生し、のちの神仏習合思想の基礎となった。