From its very beginning, the church faced two types of challenge: opposition from the outside, in the form of persecution, and corruption from the inside through heresy.
Growth of the early church
In the first centuries of its existence, the Christian church grew rapidly. At the end of the second century, we find churches all around the Mediterranean Sea. In the next few hundred years, churches are found in Britain, Spain, and India.
Initially the church consisted of Jews and “god-fearers” who already had connections with the Jewish synagogue. From the second century onward, many others join. The gospel was especially attractive to the poor, slaves, women, and other underprivileged people. But some upper-class and highly educated people also joined.
The shift from a Jewish constituency to a more Hellenistic population is reflected in early Christian writings. The debates with Judaism (e.g. Justin’s Dialogue with Trypho) gradually makes place for interactions with Hellenistic philosophies (e.g. Origen’s Against Celsus).
How the Romans viewed the church
At first, Roman society tolerated Christianity. To them it was simply another group within Judaism. Even though Judaism was repulsive for the Romans, they respected its great antiquity and allowed the Jews much freedom. It was a religio licita, an allowed religion.
But as Christians began to distance themselves from the Jews, the Romans treated Christianity like a newfangled religion. It offended on many levels and was not tolerated; it became a religio illicita.
At the same time, Christians led obviously moral life and did much good in society. For instance, they took care of the poor and of abandoned children. Because of this, many Romans respected their Christian neighbors, even though they considered them strange.
The “strangeness” of Christianity to Romans hinged on three main points. First, they did not participate in local cultural events and festivals. Christians refused to participate because these events were steeped in idolatry; but it made them look like disloyal to their community. Second, they refused to acknowledge the emperor (“Caesar”) as their lord. Third, outsiders did not exactly know what went on in church services, but there were plenty of rumors about the “love feasts”, the “holy kiss”, the “eating of flesh” and the “drinking of blood”. Thus, Christians were suspected of incest and other sexual immorality, as well as cannibalism.
Informative is the letter of Roman governor Pliny to the emperor, around 110 AD. Pliny wonders what he should do with Christians. He considers Christianity a form of madness, which cannot be tolerated; at the same time, his investigation shows that the Christians were rather harmless. They emperor tells Pliny not to persecute Christians actively, but if they are brought up on charges, they should be required to denounce their faith and sacrifice to the emperor. If they fail to do so, they must be executed.
In short, Christian believers were considered obnoxious and crazy; they were often ridiculed and ostracized.
But systematic persecutions of Christians by Romans were rare. The earliest instance was the “great fire” of Rome in 64 AD. Emperor Nero blamed the Christians and drove them out of the city. A few other cases of large-scale persecution occurred under Emperor Domitian (around 90 AD), Decian and Valerian (around 250 AD), and Diocletian (around 300 AD).
The persecutions did not stop the growth of the church. On the contrary, “the blood of the martyrs was the seed of the church.” The “Acts of Martyrs” (official reports of the execution of Christians) became popular literature. Some zealous believers even tried to be arrested so that they could die as a martyr! In this time begins the custom of collecting relics, i.e. possessions or bones of martyrs, as precious objects of veneration.
Orthodoxy and heresy
The early church had a strong sense of catholicity: the various local churches were essentially one, sharing the same beliefs worldwide. (“Catholic” means worldwide, or universal.) Over time, it became important to establish the official teaching of this catholic church community. Agreement with these official teaching is called orthodoxy. Disagreement is heterodoxy or heresy.
In the second and third centuries, the church battled various false teachings, most of them related to the identity of Jesus Christ. This resulted in a clear definition of the “orthodox” faith.
Initially, the orthodox faith was expressed informally, for instance in liturgical statements and writings of individual Christian authors. Together they form the “rule of faith” (regula fidei). Later, church councils adopted official statements to define clearly what is orthodox and what is not. Such statements are called creeds. One of these creeds was the Old Roman Creed, which became the basis for the well-known Apostles’ Creed.
Marcion and the Gnostics
The first teacher to be officially declared a heretic was Marcion. In his view, the Old Testament God who had created the material world and given the Law was evil. Jesus and his Father, the New Testament God, delivers people from this. In order to maintain his view, Marcion had to reduce the Bible to the gospel of Luke and only some of Paul’s epistles. In 144 AD, Marcion was officially excommunicated (removed from the church).
Marcion’s heresy was similar to Gnosticism, a religious philosophy that became popular in this time. They posed a dualism between the evil, material world and the good, spiritual realm. Salvation, in this view, means that people escape attachment to the material world through special spiritual knowledge (gnosis).
The Gnostics and other heretics rejected the Christian teaching that in Jesus Christ, God had assumed a physical, human body. Other heretics denied that Jesus Christ was more than just a human being. In response to these ideas, the church emphasized that Jesus is both truly God and truly man. These discussions would continue until the 400s.
The Christian canon
A canon (Greek: “ruler”) is a list of writings that are officially recognized as authoritative. The Old Testament canon was established by Jewish rabbis in the first century. Christians essentially copied this canon, although some added a number of apocryphal books that were part of their Greek version of the Old Testament.
The New Testament canon grew organically. Early in the second century, writers quote the gospels and Paul’s epistles as authorities. The first explicit list we have is the Muratorian canon (188 AD). It is already very similar to the list of 27 books we use today. The first official adoption of a canon by a church council was later, around 400 AD.
Various other writings were not included in the canon. This includes various infancy gospels, Gnostic gospels, and epistles by the second generation of Christians. In response to the Montanist heresy, which taught that authoritative revelation continued beyond the first apostles, the church declared the canon to be closed.