What exactly was the purpose of the Council of Nicea?

I am currently reading When Jesus became God: The Epic Fight over Christ's Divinity in the Last Days of Rome, which addresses this very issue.

The short answer is basically, the first council of Nicea (in 325 A.D.) was for the purpose of unifying the church under Constantine's rule.

Up until that point, the church was very fragmented, just having survived 3 centuries of persecution, including torture and death. As Constantine was interested in making Christianity the official state religion, he needed the church leaders to be unified, so there could be a single religious force in the empire.

This was the purpose of the council. Its success was quite mixed, however, and while it may have created unity on paper, it caused a lot of division and in-fighting in reality.

The First Council of Nicaea was a group of Christian bishops assembled in Nicaea in Bithynia by the Roman Emperor Constantine I in AD 325. This first council was the first effort to gain a general consensus in the church in theology.

Its main accomplishments was the settlement of the issue of the divine nature of Jesus, the Son of God; his relationship to God the Father; the construction of the first part of the Creed of Nicaea; establishing an accepted date of of Easter; and declaring the early canon law.

Wikepidea's summary of the Council's agenda:

"The Arian question regarding the relationship between God the Father and the Son (not only in his incarnate form as Jesus, but also in his nature before the creation of the world); i.e., are the Father and Son one in divine purpose only or also one in being?

The date of celebration of Pascha/Easter

The Meletian schism" - Wikepida

Although many are of the opinion that the Council of Nicea was called to prep Christianity to become the official state religion, this is not accurate. This hypothesis does not fit with what we know about the mindset of the people of that time or Constantine. It should be remembered that Constantine was not yet a baptized Christian in 325 AD (the year the council was held); rather, his mother was. Although he took a great interest in the church (and would continue to do so with greater fervor as he grew older), Constantine was not baptized or fully accepted into the church until shortly before his repose.

The Edict of Milan also did not simply give freedom to Christians: it gave freedom to all religions. So, while Christianity certainly enjoyed the favor of the court, it did not become an official state religion, especially not to the exclusion of other religions. Even the Arian group that was cut off from the church existed peacefully in the empire for another several centuries.

Constantine also did not control the council, despite popular rhetoric to the contrary. In fact, everything we know about the council indicates the exact opposite. We have no official acts from the council, but we do have writings of many of the bishops and other clergy that attended it. Eusebius of Caesarea (not to be confused with Eusebius of Nicomedia) says that Constantine did not speak or understand Greek (the language used at the council) very well, so Bishop Hosios of Spain translated into Latin for him when he (Constantine) could find time to attend the council. It is estimated that the council took place over several months, and an emperor simply wouldn't have time to attend them all.

Further evidence that Constantine did not control the council is its result. It was precisely Constantine's best friends that were condemned by the council. I have in mind here in particular Arius and Eusebius of Nicomedia (Eusebius later repented, was received by into the church, and went on to be the one to baptize Constantine).

As for the canon of scripture, it was necessary to establish at the beginning of the council which books were valid for argumentation. The question of authenticity was put to the Alexandrian party, as Alexandria was the center of learning in the world. The person generally credited as the lead researcher on the project is Athanasios the Great, whom I believe was a deacon at the time (if memory serves me). The selection of books was not, as Dan Brown might lead you to believe, done in either a conspiratorial or haphazard manner. The selections were quite reasonable, thoughtful, and well researched.

However, the selection of these books was not formally codified until the Second Oecumenical Council (381 AD). Part of the reason for this—and this is a major point missed by the majority of modern scholars—was the preference for and devotion to tradition on the part of the early church. Just as today, we argue over "what the Bible says," the early church argued over what had been handed down from the apostles and their successors. Oral tradition was considered sacred and the key to understanding the writings of any apostle or early church author. "Hold to the traditions you were taught, whether by word or our epistle," wrote the Apostle Paul. The early church believed this deeply and followed it closely. All councils, whether local, regional, or oecumenical, were considered valid only in so far as they did not deviate from the sacred tradition handed down. Nearly all arguments made at these early councils hung on whether a thing had been passed down from bishop to bishop or not.

The main arguments at the First Oecumenical Council centered precisely around oral tradition. This is very important to understand. The First Oecumenical Council DID NOT FORMULATE NEW THEOLOGY. The very idea of "formulating" new theology is a very western idea and didn't even appear in the west as a concept until much later. The early church fathers abhorred and shunned the very idea of innovation.

Then what did the council do? The council introduced new terminology to more accurately express what had already been handed down. All of the bishops but 5 agreed on what had been handed down, though it took them quite a while to decide on whether or not to use the term "h*m*ousion" (as opposed to the Arians' preference for "homiousion"). They tip-toed around this term because it had been used in a heretical way by Paul of Samosata some years earlier.

Constantine certainly did want to see the church rid of divisions—don't get me wrong. But I hope you will consider reading PRIMARY sources on this topic rather than the opinions that are currently trending and regurgitating among modern christians.