The Council of Nicaea was the first ecumenical council, and it was big one. Emperor Constantine, a recent convert to Christianity, called for the council in the summer of 325. Bishops from all over the empire as well as Asia, Persia, Palestine, Egypt, and Greece met at Nicaea. St. Athanasius counted that 318 bishops attended, as well as several hundred priests and deacons. Constantine opened the session but did not participate in any of the doctrinal matters. He real interest was uniformity across the empire.
IssuesConstantine called the council for bishops to settle on a universal statement on the relationship between God the Father and Jesus. There were two predominate camps at the time. Trinitarians believed that the Father and the Son were both God, separate persons of the same substance. Arians, named after the Libyan priest Arius, believed that the Father was greater than the Son. It also called into question Christ’s divinity by suggesting that there was a time before which Christ was created. Arius was not the only person with nontrinitarian beliefs, but he was the one who defended those beliefs at the council.
The council also addressed the dating of Easter. Originally, Easter was observed according to the Jewish calendar, falling on 14 Nisan. However, as Christianity grew away from Judaism, it was determined that Easter should not rely on the Jewish calendar and that it should always fall on a Sunday. Different areas found different ways of determining the date for Easter, meaning that the Church did not celebrate it on the same day.
On the Trinitarian issue, Arianism was condemned. The Nicene Creed was developed to explicitly clarify the Church’s position on basic beliefs, including the consubstantialism of the Father and Son. The Creed continues to be the basic statement of faith of the Church almost 1,700 years later. The council also determined that the Church should have a universal way to determine the date of Easter. However, it did not present a calculation, so different areas continued to follow different methods. The East and West continue to celebrate Easter on different dates (except when they happen to fall on the same day, like this year). The council also ruled on some finer points of the priesthood (age of ordination, marriage rules, grounds for excommunication). This doesn’t seem to be the result of a certain debate, but was perhaps brought about by the bishops getting together and seeing the differences of protocol between sees.
HeresiesWhile Trinitarianism was widely accepted, Arianism continued to have support, mainly in the Germanic north through the sixth century. As a heresy, it grows and fades, but has never really gone away. The Nicene Creed is still used to this day as a basic doctrinal threshold, but there are still groups that disagree over the Trinitarian ruling of Nicaea. Most notably are Jehovah’s Witnesses and Oneness Pentecostals.
Misc.This was the council were St. Nicholas infamously punched Arius. While I think it’s good to note that we should keep disagreements nonviolent, it’s still fun to think of badass Santa Claus. After all, there’s always that one heretic that you just want to punch in the face.