When Rome converted to Christianity, Christianity started to flourish. Many more people converted to Christianity since it was the legal thing to do and more and more people became open to the message of Christ!
However, as the Church expanded, She became open to erroneous teachings, heresies! The first major teaching that launched itself on the Church was from Arius! Arius was an Archbishop who was teaching people that Christ was not God. He was just a prophet sent by God!
The implication of this is far reaching. It means that Christ is not the Second Person of the Blessed Trinity. It means that Christ is not the person being referred to in the Gospel of John Chapter one verse one! Many millions of people accepted what Arius was teaching and so there was confusions since the apostles taught that Christ is God and is the Second person in the Trinity!
A Church council was called in the town of Nicaea to deal with Arian heresy!
A Church council is actually a general meeting of Church leaders, bishops, who have to come together to officially restate the Chruch’s position on any issue that has arisen.
In history, the Nicaean Council is actually the Second council in the history of the Church. The first council was recorded in the Acts of the Apostles 15. That council was called to deal with the idea that non Jews who are converting to Christianity needs also to be circumcised!
Some people, including St. Peter, was teaching that membership of the Church is not limited to being baptized. You need also to be circumcised!
This caused a lot of confusion. So the Apostles gathered in Jerusalem to iron things out and reconfirm what Christ taught them. In that council it was affirmed that baptism is the central sacrament of Christian initiation that allows someone to become a member of the Church of Christ that is priestly in character!
It is this type of council that was called by the Church to deal with the heresy being taught by Arius. Constantine was present at this council. Indeed he helped to organize it!
The Council of Nicaea firmly reiterated that Christ is God and is also the Second Person of the Trinity! Christ is God incarnate who is both Man and God. The two natures are united in what is known as hypostatic union. None of the natures displaced the other when he was in the world. The Church has spoken and it is final.
From then on, it became dogma, a final teaching of the Church! The Church cannot come out any time in the future to suggest that this teaching is wrong. This is becuase any dogmatic pronouncement made by the Church is actually done by the Holy Ghost and so the Holy Ghost cannot be wrong!
After this pronouncement, the Arian heresy did not stop. It festered. Many people, especially in the East (such places as Egypt, Syria and Constantinople) continued to teach that Christ was not God. There was constant bickering between those who follow the Church and those who follow Arian heresy. In fact, sometimes, it resulted in open fight in the streets.
After sometimes, the Arians modified their teaching and started to say that Christ is God only when he performed miracles and during the transfiguration! For them Christ’s God-ness comes and goes depending on the situation and whenever He is God he seizes to be man and when he is man, he seizes to be God! Also, they started to teach that God the father and God the Son are not of the same substance and so God the Son was created by God the father! But this is a form of Semi-Arianism!
Such Saints as St. Athanasius continued to fight in Alexandria Egypt, preaching everyday against the heresy of Arius and wining back many thousands of people back to the Church! Up till today, we still have those who believe strongly in the Arian heresy and sometimes we see the vestiges of Arian heresy in today’s Pentecostalism!