The Final Act
For many modern Christians, the Council of Nicaea marks a basic decision of the church about its faith. After that crucial event, all who disagree with Nicaea's insistence that the Son is one in being (homoousios) with the Father could only be considered heretics.
But that is not how people saw it at the time. The idea that Nicaea was a fundamental turning point developed gradually over the decades that followed. Modern Christians should certainly accept the church's decision for Nicaea and the Trinitarian faith, but they should know that the Spirit only slowly led Christians to the true reading of Scripture.
There are two reasons Nicaea was not originally regarded as the decisive moment that many textbooks assume. First, the idea that a creed with fixed wording might serve as a universal standard of belief had not yet developed. The council made an ad hoc decision, and it stated its faith in terms that clearly differentiated its beliefs from Arius's. But nobody at Nicaea assumed that this particular wording would stand as the fundamental Christian confession for centuries to come. Local creeds continued to be used for teaching converts and children until the next century. (One of the best examples is the "Apostles' Creed," which originated as the local creed of the Roman church.) The Council of Nicaea was well known (because of its size and its association with Emperor Constantine), but no one regarded its confession as a universal marker of orthodoxy. At that point in history, no creed was treated that way.
Second, the controversy between Arius and his bishop Alexander was the product of wider tensions in the early fourth-century church. Nicaea was one battle in a much wider war between different ways of interpreting what ...