Q: What caused other Christian groups to become separate? For example, who was John Calvin and what did he teach that a denomination is sometimes called “Calvinist”?
A: John Calvin (1509-1564) was a French reformer who broke with the Roman Catholic Church in 1533 and went on to establish what is known as the Reformed branch of Protestantism. Any group with Presbyterian or Reformed in its title is descended from Calvin’s movement. Presbyterians reject the office of bishop and see Church authority as ultimately vested in the local community.
One of the strongest beliefs in Calvinism is that individuals are predestined for salvation or for damnation. Material prosperity and social influence were often seen as signs of election by God.
Roman Catholics believe that God intends that all people be saved, but individuals can cooperate with or frustrate God’s intention. In Romans 8:29-30, St. Paul speaks of predestination in a very wide sense, assuming human cooperation with God’s grace.
Although there were heretical groups that broke off from Christianity in its first 1,000 years, it was pretty much a single group until the East/West split in 1054 A.D. This began the custom of calling the Easterners the Orthodox and the Westerners Roman Catholics. Several Oriental Orthodox Churches existed prior to 1054 A.D. There are also Eastern Catholic Churches (united with the pope but following their own liturgical rites). The Western Church split after Martin Luther’s protest began in 1517.