The question, if you really want to know, is here.
Answer to Part A:
The Mediterranean world of the 4th century CE was undergoing fundamental shifts in the organization of their political institutions and the relationship between the Roman Empire, the traditional pagan cults, and the emerging Christian church. At the same time, the church was undergoing a series of debates which sought to clarify points of doctrine which had not been fully articulated in scripture. The Council of Nicea in 325 and the Council of Constantinople of 381 produced what we now call the Nicene Creed in response to these stresses. The Nicene Creed articulated with greater clarity our understanding of the persons and relationships within the Trinity at a time when persecution of the church was decreasing yet the Roman Empire was becoming more fractured.
The unenviable task of holding the Empire together had fallen to Constantine, who with his mother, Helen, was an admirer and eventual adherent of Christianity. Although Christians had been persecuted to a greater or lesser extent since the crucifixion of Jesus, tolerance of the church had gradually increased. Constantine credited his victory at the Battle of Milvian Bridge to a Christian vision, and with the Edict of Milan in 313, tolerance of the church became official policy of the Empire. When Constantine became emperor of the whole Roman Empire, he looked to Christianity as a unifying social force.
Acting in this capacity could, however, prove challenging to the church. During centuries of persecution, Christianity had largely defined itself in opposition to external oppression. This definition left room for internal disagreement about issues which were not clearly defined in scripture. The greatest controversy surrounded how to describe the persons of the Trinity — Father, Son, and Holy Spirit — and how to characterize their relationships to one another. A group of clerics in Palestine and Syria who associated themselves with the teachings of Arius, held that God the Father begat the Son at a point in time prior to the creation of the world, making the second person of the Trinity subordinate to the first. Alexandrian Christians, followed the teaching of their bishop, who held that the Son is eternally begotten of the Father and so the two persons are equal within the Trinity. Using his authority as Emperor, Constantine called the parties to Nicaea where a council discerned that the Alexandrian understanding would be the authoritative teaching of the church.
By 380 Christianity had become the official religion of the Roman Empire, but the Empire continued to fracture. When Theodosius rose to the throne in 381, his empire consisted of the eastern half of what had once been under Rome’s control. Ruling from Constantinople, he had even greater need than Constantine for order and unity. At the same time, the work of Nicaea had not fully answered the questions raised by the doctrine of the Trinity. In 381, Theodosius called a council at Constantinople to further refine the formula set forth at Nicaea.
This council sought to address the controversy which persisted regarding the place and role of the Holy Spirit in relation to the Father and the Son. Just as Nicaea determined that the Son was equal to the Father within the Trinity, Constantinople discerned that the Holy Spirit, who proceeds eternally from the Father, is co-equal to the Father and the Son within the Trinity. (Whether the Holy Spirit also proceeds from the Son would be a discussion for later theologians.) For Christians living in the turbulent times of the 4th century CE, it would be of great comfort to know that the Holy Spirit (by which they seek to direct their lives and draw their experience of salvation) is of the same substance as the Father and the Son.
Such clarity would have been important for Theodosius as well since it brought the opportunity for greater unity and cohesion within the parts of the Empire he controlled. It would not be fair, however, to limit Theodosius’s motivations to purely political calculations. He could also have held genuine concern for the spiritual well-being of his subjects. Theodosius likely would have understood religion to be inseparable from civic affairs; therefore, the saving actions of the Holy Spirit would apply to the people collectively as much as they would to any particular individual. The articulation of the doctrine of the Trinity and the clarification of the persons of the Trinity and their relationships to one another in the Nicene Creed provided an important source of unity for the church and the Roman empire in the 4th century.
The Nicene Creed and its implications are important today because they continue to provide needed clarity and potential for unity as Christianity moves from an established, privileged place in society to being a voice among many in our civil life. Since its adoption, the Nicene Creed has articulated Christian beliefs and identity in a way that is not simply as a group which is persecuted or oppressed. While we must be ready to meet persecution or oppression should it be visited upon us, we run the risk of falsely associating the loss of privileged status with persecution if we let go of the sense of identity which is offered to us by the Nicene Creed. For instance, the passage of civil statutes allowing same-gender couples to marry may indicate the loss of Christianity’s privilege to give a traditional definition to civil marriage, but Christians need not identify ourselves as persecuted because such a law has passed.
Our sense of identity as shaped by the Nicene Creed has traditionally been understood as a corporate identity, with the Holy Spirit binding our individual salvation to our care and concern for our neighbors. Restoring this traditional identity could be helpful as we work to assuage the effects of individual consumerism on our political and social lives as well as on God’s creation. We can make common cause in this effort with believers of other faiths, if we are willing to see where we can agree. In discussions with Muslims, for example, we can affirm that we believe in one God since the Nicene Creed explicitly states that this is the case. As Christianity transitions from a position of cultural dominance to participation in a pluralistic society, we continue to need the Nicene Creed to give us a positive identity, an understanding of the interconnectedness of our lives, and a way to be in responsible conversation with other faiths.