It's more than a little disconcerting to see ignorant assertions repeatedly offered with such nonchalant authority. As has been noted more than once in these forums ...They (Council of Nicaea) chose them based off of authorship (who they thought wrote it) and doctrinal content. ...So why were the books that were Cannonized Cannonized?
There is no record of any discussion of the biblical canon at the council. The development of the biblical canon took centuries, and was nearly complete (with exceptions known as the Antilegomena, written texts whose authenticity or value is disputed) by the time the Muratorian fragment was written.
In 331 Constantine commissioned fifty Bibles for the Church of Constantinople, but little else is known (in fact, it is not even certain whether his request was for fifty copies of the entire Old and New Testaments, only the New Testament, or merely the Gospels), but some scholars believe that this request provided motivation for canon lists. In Jerome's Prologue to Judith he claims that the Book of Judith was "found by the Nicene Council to have been counted among the number of the Sacred Scriptures", which some have suggested means the Nicene Council did discuss what documents would number among the sacred scriptures, but more likely simply means the Council used Judith in its deliberations on other matters and so it should be considered canonical.
The main source of the idea that the Bible was created at the Council of Nicea seems to be Voltaire, who popularised a story that the canon was determined by placing all the competing books on an altar during the Council and then keeping the ones that didn't fall off. The original source of this "fictitious anecdote" is the Synodicon Vetus, a pseudo-historical account of early Church councils from AD 887:
The canonical and apocryphal books it distinguished in the following manner: in the house of God the books were placed down by the holy altar; then the council asked the Lord in prayer that the inspired works be found on top and--as in fact happened--the spurious on the bottom. (Synodicon Vetus, 35)
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It is not helpful to not know what you don't know.