Most Christians are familiar with a statement of faith commonly recited as part of the Eucharist service, the Nicene Creed, which resulted from the first few ecumenical, or worldwide, councils of the Church.
The first such council, held in Nicea (today Iznik, Turkey) in 325 was presided by Hosius, bishop of Corduba (today Córdoba, Spain). The council was hosted by Emperor Constantine, who sent letters to all the bishops of the known world—at the time effectively the Roman empire—inviting them to the meeting.
The Church, or loose confederation of local believing communities, already had customs and rituals and ways of organizing themselves that were more or less common to all. Some had been described in the New Testament and common usage made them normative, but there were ever new challenges and this was the first time everyone could get together without fear of persecution.
The term “church” (ekklesia) was a Greek word for a legislative body—not for a building or a community—borrowed by Christians for their decision-making community meetings; eventually, it came to mean, by extension, the whole community.
There was no professional clergy before Nicea (St. Paul notably made a living as a tent maker), but there were specialized functions within the community. Churches were headed by bishops (episkopos, literally “top head”), who were originally the only equivalent of modern clergy. They taught the faith, baptized and presided at the Supper of the Lord.
Over time, as communities grew, there would be more localized eucharistic gatherings and the bishop would delegate leadership of the Supper to one of the older men (presbyteros, “old man”); these came to be the priests, charged with very limited ritual duties.
Helping the priests were the deacons (diakonos, “servant”), who assisted during the rituals but specialized in helping solve the material problems of the members of the communities, caring for the poor, widows and orphans and so forth. There appears to be scriptural evidence that at least one of them was a woman, Phoebe, mentioned in Romans 16:1–2.
There were also other functions, including teachers and prophets, yet only the first three mentioned above were eventually recognized as ordained ministers.
However, even if the officials of the organization itself were fairly uniform everywhere, there were divergences. There were differences in ritual practices—such as whether one followed the Roman or Jewish calendar for celebrating Easter. There also arose doctrinal divergences—such as how to respond to a variety of heresies.
As noted, at this time most of the heresies concerned who Jesus the Christ was believed to be. The doctrinal issue that faced Nicea was Arianism, then new, which denied Jesus was divine; many of the contemporary heresies of Gnostic influence denied he was human.
So far, the responses had come from polemical responses by Church Fathers, such as Tertullian and others. There were a few local councils from prominent churches, such as the church of Alexandria and several churches in the Roman province of Hispania (Spain), which declared followers of several heresies as anathema, or cursed, and therefore forbidden to partake in the Supper of the Lord with the community.
In general, most of the heresies of this period sound odd to the modern Western observer. They involve thinking about the person of Jesus and the nature of God in highly intellectual ways that were distinctly Eastern, which then meant Greek, rather than Western, which then meant Latin or Roman, and generally pragmatic.
The response came in the form of symbolon, or creeds, of which there would be several in the next few hundred years. They stated the essential beliefs in ways that left little room for the heresies of the day.
The teachings of Nicea and the six councils that followed are accepted by Anglican, Catholic, Lutheran, Methodist and Orthodox and many other Christians. The teachings of these councils are deemed to summarize the essentials of the faith.