Backing up a bit to the political climate in the early part of the 4th century, we find that Rome was persecuting Christianity. Now we need to understand that the Roman Catholic Church was tied to the Roman Empire and was doing the bidding of the Roman Empire. The Roman Empire, through the Roman Catholic Church, was persecuting Christianity.
It was through Constantine’s military victory over Licinius, providing him the rule over the entire Roman Empire, that a shift occurred for Christianity. In 323, Constantine triumphed over Licinius and became the sole ruler of the Roman world. The victory enabled Constantine to move the seat of government permanently to the East, to the ancient Greek city of Byzantium (now Istanbul). He enlarged and enriched the city at enormous expense and built magnificent churches throughout the East. The new capital was dedicated as New Rome, but everyone soon called the city Constantinople.
Christians were more populous and vocal in the East than they were in Rome, so during the last 14 years of his reign, "Bullneck" could openly proclaim himself a Christian. He proceeded to create the conditions we call "state-church" and bequeathed the ideal to Christians for over a thousand years.
In 325, the Arian controversy threatened to split the newly united empire. To settle the matter, Constantine called together a council of the bishops at Nicaea, a city near the capital. He ran the meeting himself.
"You are bishops whose jurisdiction is within the church," he told them. "But I also am a bishop, ordained by God to oversee those outside the church."
Presiding at the council, Constantine was magnificent: arranging elaborate ceremony, dramatic entrances and processions, and splendid services. He was also a gifted mediator, now bringing his skill in public relations to the management of church affairs.
Unfortunately, he could not follow abstract arguments or subtle issues and often found himself at a great disadvantage at these councils.