After Constantine legalized Christianity and there was a large influx of people into the Christian religion; there was the need for official theology and a development of the theology already in place. Emperor Constantine tried to facilitate this development of an official theology, because he understood the need for order within the Church. One way he tried to help with this was by convening a meeting between all the bishops of the Church at the time; this was known as the Council of Nicea.
The Council of Nicea met in 325. The Council met to discuss several issues, one of which ended up taking over most of the meeting. On the schedule was the date of Easter, the Meletian schism, the validity of baptism by heretics, the status of the lapsed, discuss canon law, and to discuss the theology of the priest Arius. Once the meeting was underway, Eusebius of Nicomedia stood up with 22 other bishops to read the theology of Arius. Some of the bishops who had supported Arius changed their mind when they actually heard the theology read. However, some bishops still supported him and the arguments went on for two to three months. At one point Arius himself was brought in to defend himself. Nicholas of Myra was so offended by Arius’ statements on the divinity of Christ, that he actually slapped Arius across the face. He had his bishops robes striped from him and was put in jail. That night in a dream Jesus and Mary appeared to Nicholas asking why he was in jail. He replied he was in jail, “Because of my great love for you.” At this Jesus gave him the Gospel book and Mary gave him bishop robes. He was released the next day at the command of Constantine. At the end of the Council, the Arians were defeated, mostly; their beliefs lived on and would have to be dealt with for years to come. But the orthodox Church, had an answer to the problem of the Arians, they came up with a creed (professing the beliefs of orthodox Christians). This was known as the Nicene Creed (which is different than what we call the Nicene Creed today, it is less developed). Many believe the Creed was developed by Eusebius of Caesarea, the bishop of Caesarea and Palestine, based on the baptismal creed from his diocese. At the end of the meeting Constantine decreed that anyone who did not agree with the Creed would be exiled. Arius and two bishops did not agree with the Creed and were thus, exiled; however, several bishops endorsed the creed, but stated their disagreement with certain parts. The biggest example of this can be seen in Eusebius of Nicomedia, who was Constantine’s cousin and bishop; who swayed the Emperor away from the orthodox bishops to the Arian stance. After Constantine there were two Arian Emperors.
The Nicene Council set the precedence of the Ecumenical Council of the Church, when all bishops would gather together in one place to decide the important issues of the Church. There have only technically been seven Ecumenical Councils (although some churches will say there were more or less, these other councils were either only regional or only involved one church, such as the Roman Catholic Church). At many times theology would be developed or approved in the Ecumenical Councils and debates would be decided. Of course most theology would develop outside the Councils and would be accepted by the Church as it spread to different areas, much like the canonization of the Biblical texts. Most of the time a bishop or priest would write a letter or a book and explain how they understood some theological principle. These books or letters would be passed around and bishops would agree with the writings and would copy the text, thus preserving them. Ones that were not agreed with would not be copied or would have responses pointing out the problems and these responses might get copied, thus preserving them, and the Church’s theology would grow from this too. If it needed to be dealt with like the Arian controversy it would, but usually in local synods, not Ecumenical Councils. In these ways the Church developed her theological stance on issues and developed how it understood the Triune God.