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To me, the two most important things about Christianity by this date were
- It was the official religion of the Roman Empire. In other words, it had gone from being outlawed and persecuted to being the official religion.
- An orthodoxy had been established. The Council of Nicaea, for example, had gone a long way towards formally establishing what it mean to be an "official" Christian.
In the year 451 came the split of Roman Catholicism and Orthodoxy. The Coptic Church of Alexandria was known for its intellectuality so it usually was the center of the known world. Pope Leo of Rome set up a robbers council against the will of many bishops accusing St. Disocorus of Alexandria of blasphemy. Truly it was a political council because in the letter of Leo, he sent claiming Rome to be in charge. Pope Leo beat our precious Pope and ribbed his beard and plucked his teeth. That is the fruit of the faith. Without out precious fathers that suffered for the sake of preserving the right faith, the Orthodox belief would be extinct.
I am a Coptic Orthodox Christian living in the states. Most of the achievements that kept the Orthodox faith so fruitful and intact was the eccumenical councils that the Orthodox Church went through. The first being, the Council of Nicea that occurred in 325 AD which 318 bishops attended. The council put Arius on trial because he questioned the divinity of Christ. He stated that Christ was indeed God but less than God the Father. Pope Athanasius, from Alexandria defended the faith and established the creed still used today. The second council was of Constantinople in the year 381 which 150 attended; concerning "the Holy Spirit was a creation", stated Macedonius. Once again from the See of Alexandria, Pope Timothy defended the faith establishing that the HOly Spirit is equal in divinity with God the Father and God the Son. The third was the council of Ephesus in the year 431 which 200 bishopd attended. That council concerned the Constantinople bishop claimed that Christ was truly God but became God after the Epiphany. Stating that St.Mary was the Mother of Christ not the Mother of God. In Greek, Mother of God means "Theotokos". He called her "Christotokos". Pope Cyril of Alexandria defended the faith and excommunicated Nestorius.
Christianity had become a powerful force in Rome, by A.D. 392. It was practiced from one border to another. The year A.D. 392 is the year when the emperor Theodosius declared Christianity the state religion. All other religious practices have been outlawed.
The church has been organized into parishes.Each parish was led by a priest. Several parishes formed a diocese. Each diocese was led by a bishop.
Pope was the bishop in Rome and he has claimed authority over all other bishops. The Eastern churches did not accepted the authority of the Pope. The West churches in became known as the Roman Catholic Church, while the churches from the East formed the Eastern Orthodox Church.