The Nicene Creed...
The fourth century was a time of great change for the Christian Church. Most of the Church existed inside of territories belonging to the Roman Empire. The relationship between the Church and Rome had been a troubled one. The Church had experienced various forms of persecution and oppression since its very inception, and this informed the way that the Church acted/thought about itself in the world. The Church Fathers were among the noteworthy leaders and teachers of the Church in this period. They had centered their teachings on preparing for martyrdom. This all changed for the Church in 313 CE with the Edict of Milan, when Emperor Constantine established religious tolerance for the Christian Church inside of the Roman Empire. From that point on the Church only gained favor with those in power, eventually becoming enmeshed with the state. This newfound power and freedom allowed for the Church to focus on the development of its theology, as their time was not consumed by their persecution.
As the conversations and debates around proper Christian theology spread and intensified, Constantine sought to consolidate Christian thought and cement together a theology to help hold the Empire and the Church in continuity. So the emperor decided to call an assembly of Church leaders to nail down what it would mean to be a Christian. This council was called in 325 CE in Nicea, Bithynia. The primary sources tell us that there were 318 bishops in attendance, though this number is disputed by many historians as a more mythical allusion to the 318 soldiers of Abram in Genesis 14; but most of the scholars writing about the council tend to agree that there were approximately 300 participating bishops.
The council gathered, argued, debated, studied, and decided upon a creed that would govern the progression of Christian theology from that point forward.
The advantage of creedal statements [is] that almost anyone [is] capable of learning them quickly to standardize belief and put up barriers against speculation or what [is] likely to be a boundless set of disagreements about what the Christian scriptures actually mean
The Nicene Creed allowed for those who were joining the Church, of which there was acceleration after the Edict of Milan, to quickly be brought into a proper understanding of what it meant to claim Christianity as their religious affiliation. This creed also made large and complex notions, such as the Incarnation and Trinitarian theology, into relatively simple and digestible phrases. There were creeds which had come before the Nicene Creed, and there were many to follow, each of them attempting to produce a way to understand what it meant to be a Christian in their time and place. The Nicene Creed focused specifically on unifying the Church around Trinitarian and Incarnational theology. These actions led to a Church with more organization, clearly articulated doctrines, discernible practices, and a firm identity. This creed was recognized by almost all Christian churches by the end of the fifth century. There had been more localized achievements of this sort before, but never anything large-scale.
 Gonzalez, J. L, History of Christian Thought, Vol. 1, New York, NY: Abingdon-Cokesbury Press, 1991, 261.
 MacCulloch, Diarmaid, Christianity: The First Three Thousand Years, New York: Viking, 2010, 190.
 González, Justo L, The Story of Christianity, Vol. 1, New York: HarperCollins, 2010, 181.
 Ibid., 186.
 González, Justo L, Church History: An Essential Guide, Nashville: Abingdon Press, 1996, 28.
 MacCulloch, Christianity: The First Three Thousand Years, 129.
 Gonzalez, History of Christian Thought, Vol. 1, 262.
 Jolly, Karen Louise, Tradition & Diversity: Christianity in a World Context to 1500, Armonk, NY: M.E. Sharpe, 1997, 189.
 Ramshaw, Gail, Christian Worship: 100,000 Sundays of Symbols and Rituals, Minneapolis: Fortress Press, 2009, 84-5.
 González, Church History: An Essential Guide, 29.
 Hall, Stuart G., ed. Theologische Bibliothek Töpelmann : Jesus Christ Today : Studies of Christology in Various Contexts. Proceedings of the Académie Internationale des Sciences Religieuses, Oxford 25–29 August 2009, 90.
 Leith, John H, Creeds of the Churches: A Reader in Christian Doctrine, from the Bible to the Present, Atlanta: John Knox Press, 1982, 28-9.