The Catholic faith came to Korea during the Japanese invasion in 1592 when some Koreans were baptized, probably by Christian Japanese soldiers. Evangelization was difficult because Korea refused all contact with the outside world except for an annual journey to Peking to pay taxes. On one of these occasions, around 1777, Christian literature obtained from Jesuits in China led educated Korean Christians to study. A home Church began. When a Chinese priest managed to enter secretly about twelve years later, he found 4,000 Catholics, none of whom had ever seen a priest. Seven years later there were 10,000 Catholics. Religious freedom didn’t come until 1883.
In the meantime, there were horrible persecutions against the Christians. The major religion in Korea consisted of ancestor worship, and this was considered to be a cornerstone of their society. If anyone refused to take part in ancestor worship, they were considered traitors to the country, and would be killed. Obviously, Catholics would not be able to be part of that, and as a result, more than 8,000 of them were executed, and in unspeakable ways. Most of them were simple country people, whose names were known only to those closest to them. 103 of them were canonized by name, by Pope John Paul II in 1984.
O God, by whose providence the blood of the martyrs is the seed of the Church: Grant that we who remember before thee the Holy Martyrs of Korea, may, like them, be steadfast in our faith in Jesus Christ, to whom they gave obedience even unto death, and by their sacrifice brought forth a plentiful harvest; through Jesus Christ thy Son our Lord, who liveth and reigneth with thee and the Holy Spirit, one God, for ever and ever. Amen.