Not sure why I see it this way. Practically nobody else does.
It seems to me that when Constantine demanded that Christianity be reduced to a written formula (AKA belief-based system) that he changed everything.
Except that it really didn't change anything. Nicea wasn't the first time that the faith had been expressed in the language of a creed, in fact the symbol drawn up at Nicea follows the same outline that the earlier expressions of faith had used, most famously the Old Roman Symbol, itself looking like the symbols of faith already used, for example, in Baptism (c.f. St. Hippolytus baptismal creed) or as a defense of orthodoxy against heresy (c.f. St. Irenaeus' rule of faith).
What makes Nicea interesting and noteworthy is the following:
1. It attempted to address the ongoing theological crisis which was raised by Arius' teachings and actions (Arius, a former presbyter from Alexandria, who insisted that Christ was a secondary God and a creature had his ideas condemned at a local synod of bishops from Egypt; and so he left and started preaching in other parts of the eastern Empire and some accepted his ideas). It did this by insisting that the Arian formula that the Son and Logos was heteroousios (of a different substance) was heretical, and it also rejected the compromising formula of homoiousios (of a similar substance) by utilizing the formula of homoousios--the Son and Logos is of the same substance as the Father. This itself faced some scrutiny because of earlier problems and some ongoing problems with the Sabellians who used the same word in their heretical teaching that Jesus was His own Father--but the framers of the symbol at Nicea were rather clear with other language, such as that the Son is "begotten before all ages" which both denied the Arian claim that the Son was begotten in time, as a creature and also insisted that the Son is to be understood as distinct from the Father.
2. It was, until that time, the single largest gathering of bishops to any council in the history of Christianity. There had of course been many councils in the past, the first recorded council of the Church can be found in the Bible itself, the Council of Jerusalem as recorded in the 15th chapter of the Acts of the Apostles. According to Eusebius of Caesarea (himself a semi-Arian and a friend of Arius) a grand total of 318 bishops attended, the majority from the Eastern churches (only five from the Western churches, the bishop of Rome was himself not even able to attend due to his old age).
3. It's symbol provided the groundwork for the Nicene Creed as accepted at the Council of Constantinople, what is known often as the Nicene Creed is perhaps better called the Niceno-Constantinoplian Creed; the only significant difference is that the Creed as put forward by the council fathers at Constantinople expanded on a few points, namely in regard to the Holy Spirit in order to address the heretical teachings of the Pneumatomachoi (aka the Macedonians), and also brought in the language from earlier creedal language such as references to the Church, the resurrection of the dead, etc; likewise it did not retain the specific anti-Arian anathemas which were used in the Nicene symbol itself.
Outside of changing feast days and locations of historical events, he created a system where one was a member of the official religion if one believed certain facts and adopted certain practices.
Constantine didn't do anything like that. However at the Council of Nicea the council fathers did decide to finally establish a universal Paschalion (calculation of when to celebrate the Paschal Feast, more commonly called "Easter" in English); the consensus was two-fold, the Quartodeciman system was already incredibly small and generally only adhered to by a few handfuls of heretics at the time (it had at one time been the common practice of the Churches in Asia and Palestine, most notably the great St. Polycarp bishop of Smyrna had been a Quartodeciman a position which was not condemned because it was not then associated with other heresies and heretical movements); further it detached celebration of the Paschal Feast from the Jewish calendar entirely as the Jewish calendar itself had been modified in the first few centuries of the Common Era, and frequently churches from many different places while generally following the same or a similar method of calculating Pascha ended up observing the Feast at slightly different times. Thus as explained in the letter sent to the Egyptian Churches, the council had found it was in the best interest to adopt the liturgical practice of the Egyptian churches and to establish a common Paschalion for all the churches; one that did not depend on the Jewish calendar which, as noted, had itself undergone changes in recent times.
Further, any cursory reading of the pre-Nicene writings of the Church--the New Testament included--it's pretty obvious that what was of critical importance was a unity of faith shared among the churches; there was after all one faith, one baptism, etc. And so a standardization of some liturgical practices was not exactly some drastic departure from some earlier, primitive, "pristine" form of religion in the past--it was a natural outgrowth of the same Church as Christ had founded doing and being what it ought to have been.
I even suspect that this may have been the person Daniel spoke of. And think...that was a mere 300 and some years after Christ. The following years could very well be the "falling away" or "apostacy" spoken of by Paul.
I have been told for years that the falling away was the rejection of the modern American gospel.
More likely Daniel was speaking of Antiochus IV Epiphanes, who fits the bill for what Daniel speaks of--which would be more well known in Protestant circles if Bible publishers hadn't excised the Deuterocanonicals from Protestant English Bibles in the late 19th century. The relevant Maccabean history is easily read about online, and the book of 1 Maccabees is a pretty important read historically here. The king of the north was Antiochus, the king of the south was Ptolemy; the Syrian Wars were a number of conflicts fought between the Seleucids and Ptolemaic Egypt--for most of the post-Alexander period Judea was part of Ptolemaic Egypt, and generally, the Ptolemies were pretty lenient and allowed the Jews freedom of religion and practice--when the Seleucids conquered the area under the rule of Antiochus he systematically took the religious freedoms away from the Jews and attempted a program of forced Hellenization: the Jews were forbidden from circumcising their infants, from observing the Sabbath, celebrating their feast days, or performing their rites in the Temple. But what broke the camel's back was when Antiochus desecrated the Holy Temple by offering a pig as a sacrifice to Zeus in the Holy of Holies--the abomination that causes desolation. In response to these abuses and this outrageous blasphemy the brothers Judas and Jonathan Maccabeus would rise up and lead a revolt against the Seleucids and they managed to even restore sovereign rule to the Jews--and the rise of the Maccabean state allowed for an independent Israel for a time, until the conquests of the Romans, Caesar's general Pompeii conquered the region, and Antipater the Idumaen, the father of Herod the Great, was installed as king and in order to represent Rome's interests in the region. And you know the rest.
-CryptoLutheran