In AD 380 the Roman emperor Theodosius made Christianity the state religion, calling the new religion Catholic. In one generation, Christians went from being persecuted, to becoming the official religion of the Roman Empire. Between the 4th and the 6th century, much of what we know now as the faith of the Roman Catholic Church emerged. At the center of this was the powerful Bishops including the Patriarch of Rome who took on the name "Pope" by the sixth century.
Here's more information from the popular book, "Roaming Catholics: ending the wandering to embrace the wonder"
The need for a standard liturgy grew in the minds of those who felt
they were in charge. The thought was that unity of the church would
only come about by conformity. Initially there was great variety in Sunday
celebrations, language, and customs. In the seventh century, however,
Pope Gregory the Great declared that the Latin Mass in Rome was the
standard for the Western Church. Latin versus Greek would ultimately
contribute to the Great Schism in the church in AD 1054.
As it became more scripted and standardized, the Catholic Mass
emphasized the sacrificial aspect of Jesus, focusing on His death on the
cross, and grew in importance while the teaching, preaching, and symbolism
of the Passover in the Eucharist faded.
The theology of the period stressed Christ’s divinity and a harsh
divine judgment on all people who violated both the moral code as
well as the laws of the church. This theology led to the people feeling
less worthy and less likely to approach God, and instead to look to the
church as the go-between between God and man. As a result there was a
gradual separation between the clergy and laity. The church taught that
the clergy were closer to God, holy, and worthy, while the people were
separated from God, unholy, and unworthy of God’s love.
Text above from page 51 in What is a Catholic - Chapter 10 of "Roaming Catholics"
Was Peter the first Pope? Should Christians pray the Rosary? Should priests be married? These are among the provocative topics addressed in Roaming Catholics: Ending the wandering to embrace the wonder"
This thoroughly researched book presents the development of the Catholic Church in an engaging way to help Christians understand their common history shared by all. The apostle Paul referred to the church as the "Body of Christ," not the "Body of Christians." Rather than Jew and Greek, slave and free, male and female he proclaimed we are to be one in Christ.
Pastor and theologian Kenneth Behr shares his own religious evolution from a Catholic altar boy to an evangelical pastor and engages readers with a parallel story of the evolution of Catholicism.
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