Ancient Jewish prophecy referred to the coming of a king from the House of David, who would unite and rule the Tribes of Israel. When Jesus of Nazareth was born, he already had the lineage qualifications of the Messiah: he was a direct descent of King David through his mother, Mary. Though his genealogy was known at the time, it was the miracles he was believed to achieve and his ministry which prompted so many to follow him.
After his death on the cross, Jesus' disciples and family continued to spread his teachings.The earliest Christian churches, in the immediate decades following the death of Christ, comprised of simple gatherings in family homes. After all, Christianity was a crime at the time which was punishable by death, which necessitated the need for the gatherings to be humble, which promised the fledgling faith's survival.
At the time, Judaism was still the only Abrahamic faith and Christianity was merely a small sect within it. Early Christians considered themselves to be Jews who believed that Jesus of Nazareth was the Messiah; Christianity wouldn't become a religion in its own right until its further spread to the gentiles (non-Jews), which allowed for Jewish customs to become a less prominent feature. With that, Christianity developed its own unique traditions which were the basis for the Catholic Church.
The Apostolic Age refers to the time immediately after Jesus' death when his disciples and family guided the early Christians and set to work spreading Christ's message to the gentiles. The very name "Christian" was given to believers during this period (Christian is an Anglicization of the Greek word for Messiah).
The foundation of the modern Church was cemented during the Apostolic Age, following Christ's words that Peter was the "rock" of the church (which eventually gave rise to Papal succession).The disciples made decisions about the universal beliefs in Christianity, and it was then that Peter decided that gentiles converting to Christianity did not have to adhere to Jewish practices, which further separated the Christians from their Jewish brothers, and also made the religion more appealing to non-Jews.
Armenia was the first state to adopt Christianity as its official religion in the early part of the third century of the Common Era. This started a new trend; soon Ethiopia and Georgia followed. However, it was the acceptance of Christianity by Rome in 313 C.E. that would make the most profound impact.
Under the anti-tolerance policy of the Roman Empire, many Christians were martyred - - they died protecting, preserving, and professing their faith. Emperor Constantine's mother, Helena, was a Christian. The emperor grew to embrace the religion, legalizing it; eventually, he converted. It was then that he appointed his mother Augusta (the Roman and Byzantine title for empress), and allowed her to conduct a massive search of Christian artifacts in the Holy Land. During her travels, she commissioned the construction of many churches atop the sites of important occurrences in the religion, the most famous (and arguably the most significant) being the Holy Church of the Sepulchre, which is believed to be the site of the death, burial, and resurrection of Jesus Christ.
In 325, Constantine summoned the Council of Nicaea, whose purpose it was to establish a consensus amongst all of Christianity about the canonical beliefs and practices of the religion. Though it's unknown how many bishops attended, 1,800 were invited. The result was the Creed of Nicaea, which completely and firmly cemented Christianity as being an entirely separate entity from Judaism. While ancient Christians noted Jesus' humanity, and that he was a descendant of David, the Creed states that Jesus was not only the son of God, he was God. This belief is still held today by nearly two billion people, a testimony to the significance of the Council's established religious canon.