The church started with a supernatural work of God in Jerusalem. About fifty days after Jesus’ resurrection, the Holy Spirit filled the disciples, and they were empowered to preach the gospel. Acts 2 records the results of the Spirit’s coming—three thousand people were saved that day, and the church had begun (verse 41). Since that time of unity and simplicity, Christianity has separated into various branches. Today, most scholars identify three major branches of Christianity: Catholicism, Orthodoxy, and Protestantism, which are subdivided into other branches. Sometimes Anglicanism is listed as a fourth branch; sometimes it is listed as part of Protestantism.
Roman Catholicism. Catholicism is the largest and most visible branch of Christianity, and it is what many people automatically think of when they think of Christianity. Catholicism began around the fourth or fifth century AD. Before that time, Christianity had been a persecuted sect in the Roman world, but then Emperor Constantine provided religious toleration with the Edict of Milan in AD 313. After Christians received religious freedom, there began a consolidation of church power in Rome, a tendency on the part of the Roman bishop to call himself “Pope” (“Father”), and an influx of new church members who brought with them elements of their pagan religions. By the time the fifth century rolled around, several extra-biblical Roman Catholic practices had been established, including celibacy for priests. Although the church always had dissenters to the authority wielded by Rome, Catholicism remained the dominant branch of Christianity for six hundred years.
The Roman Catholic Church can be divided into the Latin Church and the Eastern Catholic churches, such as the Armenian Catholic Church, the Macedonian Catholic Church, the Syriac Catholic Church, and the Eritrean Catholic Church. There are other Catholic churches that remain independent of the Roman Church, such as the Celtic Catholic Church, the Free Catholic Church in Germany, and the Polish National Catholic Church.
Eastern Orthodoxy. The Eastern Orthodox Church officially began in 1054 with the Great Schism. That event was precipitated by the dual excommunications of Pope Leo IX (of the Western or Roman Church) and Patriarch Michael I (of the Eastern Church). Leading up to the Schism was a long history of disagreements over papal authority, the wording of the Nicene Creed, and who had spiritual jurisdiction over the Balkans.
The Eastern Orthodox Church is not a single church but rather a family of thirteen self-governing bodies, denominated by the nation in which they are located. These include the Greek Orthodox Church, the Russian Orthodox Church, the Coptic Orthodox Church, and the Finnish Orthodox Church.
Protestantism. The Protestant movement began in 1517 with the Reformation led by Martin Luther, Ulrich Zwingli, and John Calvin, who attempted to reform the Roman Catholic Church. The list of needed reforms was long—abuses of power and unbiblical doctrines were commonplace in the Roman Church. When it became apparent that church leaders were going to resist reform at all costs, various groups began to splinter away from Catholicism: the Lutheran Church took its name from Martin Luther, the German leader of the Reformation. The Presbyterians in Scotland followed the leadership of John Knox. The Anabaptists distinguished themselves by practicing believer’s baptism, rather than infant baptism. Anglicanism began in England due to a non-theological dispute between the Pope and King Henry VIII.
Other churches grouped under the Protestant movement include the Methodist Church (founded by John Wesley, who came out of Anglicanism), Amish and Mennonite churches (the spiritual heirs of the Anabaptists), Baptist churches, non-denominational churches, and Pentecostal churches.
The doctrinal differences between Roman Catholicism and Eastern Orthodoxy are serious enough to have kept those two branches of Christianity separate for almost 1,000 years. The crucial differences between those two groups and Protestants are likewise substantial and far-reaching. Ultimately, there is only one church; the Body of Christ is made up of all those who by faith in Christ are born again and have the Holy Spirit indwelling them. “There is one body and one Spirit, just as you were called to one hope when you were called; one Lord, one faith, one baptism; one God and Father of all, who is over all and through all and in all” (Ephesians 4:4–6).