Religion in the ancient world was local and particular. The monotheism of the Jewish faith and the standards of Greek philosophy prepared the way for the growth of Christianity—the universal faith.
Jesus of Nazareth was born to poor Jewish parents under the legal authority of Caesar Augustus—who was declared in his lifetime to be the son of a god and the savior of his people. The great challenge of the early Christians was to explain the audacious message of the Incarnation—that the true God of the Universe entered the world as a baby in Bethlehem.
Jesus was born into the long history of Judaism, which through the centuries before his birth, included being conquered, exiled, and ruled by foreigners. But this meant that Judaism and its messianic promise were familiar to many cultures, including the Greeks and the Romans.
Jesus performed miraculous healing, encouraged friendliness, and preached peace. Yet the Romans crucified Him because they, and the Jewish leaders, feared His claim to be God would disrupt the order and peace.
The apostles spread the Gospel throughout the Roman Empire after Christ’s death and trained others to preach the good news. As Christianity spread, many of the leading Christian apologists clarified their faith by forming credal statements of belief.
Most Romans were suspicious of this new religion because Christians refused to partake in pagan rituals and services that the Romans believed were necessary for good order. And unlike the Jews, the Christians did not have a long history or tradition.
Persecutions eventually spread throughout the Empire and were mandated by the emperors even as the Empire went through a century of chaos and instability. Many leading Christians began to defend their faith more vigorously, which also led to disputes and schisms between believers.
The emperor Diocletian managed to bring some momentary peace and stability to Rome by splitting the Empire under four emperors in what is known as the tetrarchy. But he blamed the Christians for the unrest Rome had faced and increased the persecutions.