Catholicism entered Korea as a subject of study before it arrived as a mission. In the late eighteenth century scholars of the Silhak movement obtained Chinese-language Catholic works from the annual embassy to Beijing and debated them as philosophy. In 1784 one of them, Yi Seung-hun, was baptised in Beijing and returned to baptise others. For roughly a decade the resulting community ran its own sacramental life, appointing men to celebrate and to hear confessions, until enquiry to the bishop in Beijing established that this was not permitted and the practice was stopped.
A church founded by readers rather than by missionaries had two consequences. It was lay-led and literate from the start, and it was politically exposed, because a Korean who accepted the prohibition on ancestral rites was refusing the central obligation of Joseon social order. The persecutions followed: 1801, 1839, 1846 and, most severely, 1866, when thousands were killed.
Kim Taegon was born into this. His family had been Catholic for two generations, his great-grandfather died in prison for it, and his father was executed in 1839. Chosen as a boy along with two companions to train for the priesthood, he was taken overland to Macau, studied there through years of upheaval, and returned by way of Manchuria and the Yellow Sea, mapping approaches by which priests might enter a country that admitted none.