There were key differences between the Roman Catholic Church in the west, and the Byzantine Church in the East. The geographical reach and boundaries is the most obvious. The Roman church had its greatest influence in Western Europe while the Eastern church expanded into Southeast Europe, North Africa, the Middle East and Asia Minor. This led to different languages being used in official church matters. The Roman Catholic Church used Latin in official church affairs, while the Byzantine Church utilized Greek.
The political organization of the church was also different with the Catholic Church accepting the Pope (previously Archbishop of Rome) as the highest authority, while the Byzantine church recognized four archbishops as the authority of the church. Before the East-West Schism, there were five archbishops that served as a type of committee to govern the church.
There were some differences in how the two churches understood key figures in the Christian faith. The central figure in Christianity is Jesus Christ. The Byzantine Church tended to emphasize the divinity of Christ, while the Roman church placed emphasis on his humanity. That is not to say that either church did not understand Jesus as having both qualities. Mary is also viewed differently by the churches as the Catholics did not believe Mary was born with original sin, while the Byzantine Church accepted the opposite as true. There were Catholic saints that were not recognized by the Byzantine Church, and vice-versa.
The use of iconography was a major point of contention between the two churches. The Eastern Church adorned their churches with religious icons and followers placed icons in their homes and prayed to them. The Roman Catholic church saw this as an abomination and the equivalent of idol worship.
Other differences included rules for clergy, bread used for service, the infallibility of the archbishops and the concept of purgatory.