This study investigates the events leading up to the 1839 Gihae Persecution, focusing on the letters and reports of three French missionaries—Imbert, Maubant, and Chastan—who were martyred in 1839, and Kim Dae-geon, who was martyred in 1846. By comparing these letters and reports with official Korean records, this study reexamines and corrects translation errors found in previous works. According to these letters and reports, Kim Yu-geun, a key figure in the Andong Kim clan government, played a central role in protecting Catholicism from persecution during his tenure. One notable example is his effort to prevent the Nam Eung-jung rebellion of 1836–37 from being linked to Catholicism. Although it is said that Kim Yu-geun received a Catholic baptism on his deathbed, his devotion to the faith seems uncertain. His favorable stance towards Catholicism appears to stem more from personal aspirations for the prosperity of the royal family and his clan, his desire for blessings regarding his own life, and his curiosity about Western relics and learning. During the 1839 Gihae Persecution, Kim Yu-geun fell into a coma due to illness, and efforts to mitigate the persecution were led by Kim Jeong-hui and Cho Byeong-hyeon. Despite their attempts, both were forced to resign from their official positions—Cho Byeong-hyeon after two months as the Minister of Justice (Hyeongjo Panseo) and Kim Jeong-hui after three months as Vice Minister of Justice (Hyeongjo Champan)—due to power struggles in the court following Kim Yugeun’s incapacitation. Although Kim Dae-geon referred to Kim Jeonghui as a "catechumen" of Catholicism, Kim Jeong-hui's sympathetic stance towards Catholicism seems to have been influenced by his close relationship with Kim Yu-geun, as well as his interest in both Northern and Western studies. However, his commitment to Catholicism was unstable and variable.