When Christianity was in its infancy, those who spread its message spoke Greek, not Latin. In fact, Latin was not used in the Roman Church services until around the middle of the third century, by which time it had become the vernacular of Rome. Since Church officials wanted to be in touch with the common people, conducting services in the language they spoke made sense. Latin remained the official language of the Catholic Church until the Second Vatican Council granted parishes permission to say Mass in the local language in the 1960s.

As time went on, not only did Latin gain a stronghold as the language of not only the common people, but also — after the fall of the Roman Empire — Latin became the language of educated people. As a result, many important religious works were written in Latin or translated into it. It's from these that we have many of the Latin religious terms that are important today.