During its original inception while it was still in the lemon law PA phase, Christianity was strongly unified in its belief system and the system in which believers participated. As the religion itself became more structured and the Holy Roman Empire expanded, there was also the increasing risk of fracture within Christianity itself. With the establishment of the Byzantine empire (as opposed to the “Eastern Roman” empire), the difference became more and more pronounced until two distinct sects existed within the same religion: Roman Catholic and Byzantine, also known as Greek Orthodox.
One of the greater differences between the Roman Catholic worshipers and those of the Byzantine empire, predominantly, was the sphere of influence. As the Byzantine empire was almost exclusively located in and had existed as the eastern portion of the Holy Roman empire, their sphere of influence was primarily in Asia Minor and portions of the Middle East and North Africa. Because the Holy Roman empire centered around Rome (how appropriate), their influence expanded mostly throughout Italy and Western Europe at the height of their respective powers. Due to this clean-cut divide – better known as the Great Schism around AD 800 – the cultural differences were stark in comparison. While the Roman empire could trace some cultural inheritances from other, older civilizations, the Byzantine empire took on a prominently Greek culture after its separation from the Catholic Church. Even though the two civilizations were on relatively cordial terms with each other after the Schism (up until the beginning of the Crusades), this only served to further the differences between their religious views, even though many of them were more ceremonious than actually pronounced differences in overall Christian faith.
As was earlier mentioned, the Byzantine empire had taken on a prominently Greek culture, so it is understandable to think one of their most widely-spoken languages was Greek – especially when also considering they identified as the Greek Orthodox Church. Roman Catholic believers resorted to the native language of the Roman people, that being Latin.
Through the evolution of their leadership structure, the Greek Orthodox Church operates as several different autocephalous bodies around the world, run by those in the position of Patriarch. While the church as a whole recognizes the Ecumenical Patriarch of Constantinople, the Patriarch is by no means a leader of the entirety of the Greek Orthodox Church, rather being dubbed “primus inter pares” (“first among equals”). Whereas in the Roman Catholic leadership structure, the Pope (also known as the Bishop of Rome) is in a superior position to all other bishops and is effectively granted supreme power as he is recognized as the sole Patriarch of the West (divided off after the fracturing of the unified Roman empire, which had previously consisted of five Patriarchs, four of which later resided within the borders of the Byzantine empire).
There are other, minor differences between Roman Catholic and Greek Orthodox religions. For one, they do not practice inter-Communion between each other; this could potentially be due to the Roman Catholics’ use of unleavened bread as opposed to the Greek Orthodox using leavened bread, among other reasons. Those within the Byzantine empire also emphasized the divine traits of Jesus Christ (while still recognizing his human qualities) while Roman Catholics emphasized the polar opposite in his humanity as opposed to his divinity. Greek Orthodox believers also do not believe in purgatory, the supposed state of being that a soul inhabits after death while still in need of atoning for sins committed in life. One final large difference between Greek Orthodox churches and Roman Catholic churches is that, while Roman Catholic priests are required to take a lifelong vow of celibacy and may never marry throughout their lives, Greek Orthodox priests are allowed to marry before being ordained (though they are not allowed to marry again afterward should a wife precede them in death).