THE ROLE OF CONSTANTINE
We are dependent, in large measure, on the words of Eusebius of Caesarea for our knowledge of many of the events at the council. This is somewhat unfortunate, because Eusebius, the first "church historian," was a partisan participant as well. Historians recognize that his viewpoint is influenced by his desire for the favor of the Emperor and by his own political and theological goals and positions. Philip Schaff, in reproducing Eusebius’s description of the entrance of the Emperor into the council, speaks of Eusebius’s "panegyrical flattery."  Eusebius presents Constantine in the highest possible terms so as to enhance his own position.
What really was Constantine’s role? Often it is alleged (especially by Jehovah’s Witnesses, for example) that, for whatever reasons, Constantine forced the "same substance" view upon the council,  or, at the very least, insured that it would be adopted. This is not the case. There is no question that Constantine wanted a unified church after the Council of Nicea. But he was no theologian, nor did he really care to any degree what basis would be used to forge the unity he desired. Later events show that he didn’t have any particular stake in the term homoousios and was willing to abandon it, if he saw that doing so would be of benefit to him. As Schaff rightly points out with reference to the term itself, "The word...was not an invention of the council of Nicea, still less of Constantine, but had previously arisen in theological language, and occurs even in Origen [185-254] and among the Gnostics...."  Constantine is not the source or origin of the term, and the council did not adopt the term at his command.
THE DECISION AND THE CREED
The truth of how the council came to use the term is not difficult to discern. Athanasius notes that the gathered bishops truly desired to express their faith in primarily scriptural language, and they tried to do so. But every time they came up with a statement that was limited solely to biblical terms, the Arians would find a way of "reading" the statement so as to allow for agreement.  They were forced to see that they needed to use a term that could not be misunderstood, that would clearly differentiate between a belief in the full deity of Christ and all those positions that would compromise that belief. Therefore, they focused on the term homoousios as being completely antithetical to the Arian position, and at the same time reflective of the scriptural truth that Jesus Christ is not a creature, but is fully God, incarnate deity.
The "orthodox" party had to express clearly to the "middle group" that by the use of the term homoousios they were not in any way attempting to give aid and comfort to the modalists and Sabellians in the East who continued to teach their errors even in the days of Nicea. They were not compromising the existence of three Persons, but were instead safeguarding the full deity of the Persons, and in particular, the Son.13 The resulting creed, signed by all but Arius and two bishops, was quite clear in its position:
We believe...in one Lord Jesus Christ, the Son of God, begotten from the Father, only-begotten, that is, from the substance of the Father, God from God, light from light, true God from true God, begotten, not made, of one substance (homoousios) with the Father, through Whom all things were made....
The creed also contained the "anathema" (i.e., condemnation) for those who rejected these truths, and for the first time, such anathemas carried with them civil repercussions. Arius and some of his followers were banished, even though for a short time. This set a precedent that eventually would have tremendous impact on culture and church, but it is also a separate issue from the theological proclamation of the council.
Nicea did not come up with something "new" in the creed. Belief in the deity of Christ was as old as the apostles themselves, who enunciated this truth over and over again.  References to the full deity of Christ are abundant in the period prior to the Council of Nicea. Ignatius (died c. 108), the great martyr bishop of Antioch, could easily speak of Jesus Christ as God at the opening of the second century. More than once Ignatius speaks of Jesus Christ as "our God."  When writing to Polycarp he can exhort him to "await Him that is above every season, the Eternal, the Invisible, (who for our sake became visible!), the Impalpable, the Impassible, (who for our sake suffered!), who in all ways endured for our sake."  Ignatius shows the highest view of Christ at a very early stage, when he writes to the Ephesians: "There is only one physician, of flesh and of spirit, generate and ingenerate, God in man, true Life in death, Son of Mary and Son of God, first passible and then impassible, Jesus Christ our Lord." 
Melito of Sardis (c. 170-180), a much less well-known figure, was tremendously gifted in expressing the ancient faith of the church regarding the deity of Christ:
And so he was lifted up upon a tree and an inscription was provided too, to indicate who was being killed. Who was it? It is a heavy thing to say, and a most fearful thing to refrain from saying. But listen, as you tremble in the face of him on whose account the earth trembled. He who hung the earth in place is hanged. He who fixed the heavens in place is fixed in place. He who made all things fast is made fast on the tree. The Master is insulted. God is murdered. The King of Israel is destroyed by an Israelite hand. 
Nicea was not creating some new doctrine, some new belief, but clearly, explicitly, defining truth against error. The council had no idea that they, by their gathering together, possessed some kind of sacramental power of defining beliefs: they sought to clarify biblical truth, not to put themselves in the forefront and make themselves a second source of authority.
This can easily be seen from the fact that Athanasius, in defending the Nicene council, does so on the basis of its harmony with Scripture, not on the basis of the council having some inherent authority in and of itself. Note his words: "Vainly then do they run about with the pretext that they have demanded Councils for the faith’s sake; for divine Scripture is sufficient above all things; but if a Council be needed on the point, there are the proceedings of the Fathers, for the Nicene Bishops did not neglect this matter, but stated the doctrines so exactly, that persons reading their words honestly, cannot but be reminded by them of the religion towards Christ announced in divine Scripture." 
The relationship between the sufficient Scriptures and the "Nicene Bishops" should be noted carefully. The Scriptures are not made insufficient by the council; rather, the words of the council "remind" one of the "religion towards Christ announced in divine Scripture." Obviously, then, the authority of the council is derivative from its fidelity to Scripture.
While the creed of the council was its central achievement, it was not the only thing that the bishops accomplished during their meeting. Twenty canons were presented dealing with various disciplinary issues within the church. Of most interest to us today was the sixth, which read as follows:
Let the ancient customs in Egypt, Libya, and Pentapolis prevail, that the Bishop of Alexandria have jurisdiction in all these, since the like is customary for the Bishop of Rome also. Likewise in Antioch and the other provinces, let the Churches retain their privileges. 
This canon is significant because it demonstrates that at this time there was no concept of a single universal head of the church with jurisdiction over everyone else. While later Roman bishops would claim such authority, resulting in the development of the papacy, at this time no Christian looked to one individual, or church, as the final authority. This is important because often we hear it alleged that the Trinity, or the Nicene definition of the deity of Christ, is a "Roman Catholic" concept "forced" on the church by the pope. The simple fact of the matter is, when the bishops gathered at Nicea they did not acknowledge the bishop of Rome as anything more than the leader of the most influential church in the West. 
Modern Christians often have the impression that ancient councils held absolute sway, and when they made "the decision," the controversy ended. This is not true. Though Nicea is seen as one of the greatest of the councils, it had to fight hard for acceptance. The basis of its final victory was not the power of politics, nor the endorsement of established religion. There was one reason the Nicene definition prevailed: its fidelity to the testimony of the Scriptures.
During the six decades between the Council of Nicea and the Council of Constantinople in 381, Arianism experienced many victories. There were periods where Arian bishops constituted the majority of the visible ecclesiastical hierarchy. Primarily through the force of political power, Arian sympathizers soon took to undoing the condemnation of Arius and his theology. Eusebius of Nicomedia and others attempted to overturn Nicea, and for a number of decades it looked as if they might succeed. Constantine adopted a compromising position under the influence of various sources, including Eusebius of Caesarea and a politically worded "confession" from Arius. Constantine put little stock in the definition of Nicea itself: he was a politician to the last. Upon his death, his second son Constantius ruled in the East, and he gave great aid and comfort to Arianism. United by their rejection of the homoousion, semi-Arians and Arians worked to unseat a common enemy, almost always proceeding with political power on their side.
Under Constantius, council after council met in this location or that. So furious was the activity that one commentator wrote of the time, "The highways were covered with galloping bishops."  Most importantly, regional councils meeting at Ariminum, Seleucia, and Sirmium presented Arian and semi-Arian creeds, and many leaders were coerced into subscribing to them. Even Liberius, bishop of Rome, having been banished from his see (position as bishop) and longing to return, was persuaded to give in and compromise on the matter. 
During the course of the decades following Nicea, Athanasius, who had become bishop of Alexandria shortly after the council, was removed from his see five times, once by force of 5,000 soldiers coming in the front door while he escaped out the back! Hosius, now nearly 100 years old, was likewise forced by imperial threats to compromise and give place to Arian ideas. At the end of the sixth decade of the century, it looked as if Nicea would be defeated. Jerome would later describe this moment in history as the time when "the whole world groaned and was astonished to find itself Arian." 
Yet, in the midst of this darkness, a lone voice remained strong. Arguing from Scripture, fearlessly reproaching error, writing from refuge in the desert, along the Nile, or in the crowded suburbs around Alexandria, Athanasius continued the fight. His unwillingness to give place — even when banished by the Emperor, disfellowshipped by the established church, and condemned by local councils and bishops alike — gave rise to the phrase, Athanasius contra mundum: "Athanasius against the world." Convinced that Scripture is "sufficient above all things,"  Athanasius acted as a true "Protestant" in his day.  Athanasius protested against the consensus opinion of the established church, and did so because he was compelled by scriptural authority. Athanasius would have understood, on some of those long, lonely days of exile, what Wycliffe meant a thousand years later: "If we had a hundred popes, and if all the friars were cardinals, to the law of the gospel we should bow, more than all this multitude." 
Movements that depend on political favor (rather than God’s truth) eventually die, and this was true of Arianism. As soon as it looked as if the Arians had consolidated their hold on the Empire, they turned to internal fighting and quite literally destroyed each other. They had no one like a faithful Athanasius, and it was not long before the tide turned against them. By A.D. 381, the Council of Constantinople could meet and reaffirm, without hesitancy, the Nicene faith, complete with the homoousious clause. The full deity of Christ was affirmed, not because Nicea had said so, but because God had revealed it to be so. Nicea’s authority rested upon the solid foundation of Scripture. A century after Nicea, we find the great bishop of Hippo, Augustine, writing to Maximin, an Arian, and saying: "I must not press the authority of Nicea against you, nor you that of Ariminum against me; I do not acknowledge the one, as you do not the other; but let us come to ground that is common to both — the testimony of the Holy Scriptures." 
Why do Christians believe in the deity of Christ today? Is it because they have been forced to do so by legislated theology from councils and popes? No, it is because the Scriptures teach this truth. When orthodox believers affirm the validity of the creed hammered out at Nicea, they are simply affirming a concise, clear presentation of scriptural truth. The authority of the Nicene creed, including its assertion of the homoousion, is not to be found in some concept of an infallible church, but in the fidelity of the creed to scriptural revelation. It speaks with the voice of the apostles because it speaks the truth as they proclaimed it. Modern Christians can be thankful for the testimony of an Athanasius who stood for these truths even when the vast majority stood against him. We should remember his example in our day.
1 The Council of Nicea did not take up the issue of the canon of Scripture. In fact, only regional councils touched on this issue (Hippo in 393, Carthage in 397) until much later. The New Testament canon developed in the consciousness of the church over time, just as the Old Testament canon did. See Don Kistler, ed., Sola Scriptura: The Protestant Position on the Bible (Morgan, PA: Soli Deo Gloria Publications, 1995).
2 See Joseph P. Gudel, Robert M. Bowman, Jr., and Dan R. Schlesinger, "Reincarnation — Did the Church Suppress It?" Christian Research Journal, Summer 1987, 8-12.
3 Gordon Rupp, Luther’s Progress to the Diet of Worms (New York: Harper and Row Publishers, 1964), 66.
4 Much has been written about Constantine’s religious beliefs and his "conversion" to Christianity. Some attribute to him high motives in his involvement at Nicea; others see him as merely pursuing political ends. In either case, we do not need to decide the issue of the validity of his confession of faith, for the decisions of the Nicene Council on the nature of the Son were not dictated by Constantine, and even after the Council he proved himself willing to "compromise" on the issue, all for the sake of political unity. The real battle over the deity of Christ was fought out in his shadow, to be sure, but it took place on a plane he could scarcely understand, let alone dominate.
5 Later centuries would find the idea of an ecumenical council being called by anyone but the bishop of Rome, the pope, unthinkable. Hence, long after Nicea, in A.D. 680, the story began to circulate that in fact the bishop of Rome called the Council, and even to this day some attempt to revive this historical anachronism, claiming the two presbyters (Victor and Vincentius) who represented Sylvester, the aged bishop of Rome, in fact sat as presidents over the Council. See Philip Schaff’s comments in his History of the Christian Church (Grand Rapids: Eerdmans, 1985), 3:335.
6 Athanasius’s role at the council has been hotly debated. As a deacon, he would not, by later standards, even be allowed to vote. But his brilliance was already seen, and it would eventually fall to him to defend the decisions of the Council, which became his lifelong work.
7 The Latin translation is consubstantialis, consubstantial, which is the common rendering of the term in English versions of the final form of the Nicene Creed.
8 Modalism is the belief that there is one Person in the Godhead who at times acts as the Father, and other times as the Son, and still other times as the Spirit. Modalism denies the Trinity, which asserts that the three Persons have existed eternally.
9 Schaff, 3:624.
10 The only basis that can be presented for such an idea is found in a letter, written by Eusebius of Caesarea during the council itself to his home church, explaining why he eventually gave in and signed the creed, and agreed to the term homoousios. At one point Eusebius writes that Constantine "encouraged the others to sign it and to agree with its teaching, only with the addition of the word ‘consubstantial’ [i.e., homoousios]." The specific term used by Eusebius, parakeleueto, can be rendered as strongly as "command" or as mildly as "advise" or "encourage." There is nothing in Eusebius’s letter, however, that would suggest that he felt he had been ordered to subscribe to the use of the term, nor that he felt that Constantine was the actual source of the term.
11 Schaff, 3:628.
12 Someone might say that this demonstrates the insufficiency of Scripture to function as the sole infallible rule of faith for the church; that is, that it denies sola scriptura. But sola scriptura does not claim the Bible is sufficient to answer every perversion of its own revealed truths. Peter knew that there would be those who twist the Scriptures to their own destruction, and it is good to note that God has not deemed it proper to transport all heretics off the planet at the first moment they utter their heresy. Struggling with false teaching has, in God’s sovereign plan, been a part of the maturing of His people.
13 For many generations misunderstandings between East and West, complicated by the language differences (Greek remaining predominate in the East, Latin becoming the normal language of religion in the West), kept controversy alive even when there was no need for it.
14 Titus 2:13, 2 Pet. 1:1, John 1:1-14, Col. 1:15-17, Phil. 2:5-11, etc.
15 See, for example, his epistle to the Ephesians, 18, and to the Romans, 3, in J. B. Lightfoot and J. R. Harmer, eds., The Apostolic Fathers (Grand Rapids: Baker Book House, 1984), 141 and 150.
16 Polycarp 3, The Apostolic Fathers, 161.
17 Ephesians 7, The Apostolic Fathers, 139.
18 Melito of Sardis, A Homily on the Passover, sect. 95-96, as found in Richard Norris, Jr., The Christological Controversy (Philadelphia: Fortress Press, 1980), 46. This homily is one of the best examples of early preaching that is solidly biblical in tone and Christ-centered in message.
19 Athanasius, De Synodis, 6, as found in Philip Schaff and Henry Wace, eds., Nicene and Post Nicene Fathers, Series II (Grand Rapids: Eerdmans, 1983), IV:453.
20Nicene and Post Nicene Fathers, Series II, XIV:15.
21 For those who struggle with the idea that it was not "Roman Catholicism" that existed in those days, consider this: if one went into a church today, and discovered that the people gathered there did not believe in the papacy, did not believe in the Immaculate Conception of Mary, the Bodily Assumption of Mary, purgatory, indulgences, did not believe in the concept of transubstantiation replete with the communion host’s total change in accidence and substance, and had no tabernacles on the altars in their churches, would one think he or she was in a "Roman Catholic" church? Of course not. Yet, the church of 325 had none of these beliefs, either. Hence, while they called themselves "Catholics," they would not have had any idea what "Roman Catholic" meant.
22 Ammianus Marcellinus, as cited by Schaff, History of the Christian Church (Grand Rapids: Eerdmans, 1985), III:632.
23 For a discussion of the lapse of Liberius, see Schaff, III:635-36. For information on the relationship of Liberius and the concept of papal infallibility, see George Salmon, The Infallibility of the Church (Grand Rapids: Baker Book House, 1959), 425-29, and Philip Schaff, The Creeds of Christendom (Grand Rapids: Baker Book House, 1985), I:176-78.
24 Jerome, Adversus Luciferianos, 19, Nicene and Post Nicene Fathers, Series II, 6:329.
25 Athanasius, De Synodis, 6, Nicene and Post Nicene Fathers, Series II, 4:453.
26 I credit one of my students, Michael Porter, with this phraseology.
27 Robert Vaughn, The Life and Opinions of John de Wycliffe (London: Holdworth and Ball, 1831), 313. See 312-17 for a summary of Wycliffe’s doctrine of the sufficiency of Scripture.
28Augustine, To Maximim the Arian, as cited by George Salman, The Infallibility of the Church (Grand Rapids: Baker Book House, 1959), 295.