Why did Kangxi allow Roman Catholic missionaries to work in China in 1692?

The Kangxi emperor granted official permission for the propagation of Roman Catholicism in 1692 primarily due to his appreciation for the cultural and scientific contributions of the Jesuit missionaries residing in China.1

Kangxi was deeply interested in learning and technology, and he employed Jesuits to assist in various imperial projects. These contributions included:

• Scientific Expertise: Missionaries taught the emperor geometry and mathematics, served as directors of the Imperial Observatory, and compiled the official calendar of the empire.1
• Cartography: Under the emperor's orders, Jesuits conducted extensive trigonometric surveys to create an accurate atlas of the empire, the Huangyu quanlantu.1
• Military Technology: Jesuits were responsible for the production of cannons that proved effective in military campaigns against rebellious forces.1
• Personal Gratitude: The emperor’s favor was further solidified when Jesuit missionaries successfully cured him of malaria, leading him to provide them with a residence in the imperial city and to build a church for them in Beijing.1