Final answer:
The primary language of the Mass in Western Christianity was Latin, which was the unifying language for the Bible and liturgy under the Latin Church's dominion, with the Pope's authority.
Step-by-step explanation:
The primary language of the Mass, which refers to the Christian ceremony also known as the Eucharist, was Latin. Throughout the Roman Empire and well into the medieval period, Latin served as the language of the educated elite and the church in Europe, west of the Adriatic Sea. The Latin Church recognized the authority of the Pope and insisted on the use of Latin for the Bible and the liturgy, rather than the various local languages. The legacy of Latin influenced various Romance languages, and it remained a unifying factor in religious practices and scholarly communication across Europe for many centuries. In contrast, the eastern realm under the Byzantine Empire used Greek as the language of the church and state. This underlying linguistic divide was a part of the wider cultural and ecclesiastical differences between the Eastern and Western branches of Christianity.