Choe Je-u came from an impoverished branch of a scholarly family, barred by the circumstances of his birth from the examination path, and he spent years travelling and trading before returning to Gyeongju. Korea in 1860 had been shaken by news of the Anglo-French occupation of Beijing, by repeated famine and epidemic, and by the spread of Catholicism under persecution. He described what happened to him in the fourth month of that year as a sudden trembling, a voice identifying itself as the Lord of Heaven, and the gift of a talisman and an incantation for healing.
He called what he taught Donghak, Eastern Learning, defining it against Seohak, the Western Learning of the Catholic missions. The opposition is real, and the borrowing is obvious and he did not hide it: a single supreme heavenly lord addressed directly, a written scripture, a congregation. What he set against the Western version was the doctrine that the heavenly lord is borne within every person, so that serving heaven means serving people, and that the truth in question is Korean rather than imported.
The practice was accessible in a way that examination learning was not. A twenty-one syllable incantation, recited; talismanic writing burned and taken in water; and a body of hymns composed in vernacular Korean and meant to be sung, so that people who could not read classical Chinese possessed the teaching directly. That combination is what made the movement spread, and what made the authorities regard it as dangerous.