In a discussion recently about liturgy I was faced with the opinion that during the times between the the time of the Church Fathers and the Middle Ages that the character of the Mass was perverted in the name of clericalism and elitism, primarily by the Roman Emperor Constantine with the collusion of the Pope, who was Sylvester I (and not actually in attendance.)
Constantine did this, the narrative goes because he was seeking to accumulate power, or at least consolidate his power over the Roman Empire. So the narrative goes the laity were excluded from the sanctuary and Latin was enshrined in the Mass in an effort to exercise control over the faithful.
This is not a new narrative. It has been used by Protestants for centuries. In the pre-Vatican II era it was picked up by dissident Catholic theologians and widely used to justify everything form the wreck-ovations of the churches to the army of laity who now minister at Mass.
I will start by stating that contemporary pagan and Christian authors laud Constantine. Eusebius, Bishop of Caesarea, and Church Father wrote a basically unfinished work on Constantine after his death, which was considered the standard on the Emperor's life until the Reformation, when later pagan sources were brought forward in an attempt to discredit him. They were written during the time of the Emperor Julian, called the apostate, who was a pagan and the last Emperor of Constantine's line. Modern secular interpretations of Constatine have ignored the contemporary sources and leaned heavily on the post reformation sources, in the interest of besmirching the Church, and traditional Catholic practices.
Certainly Constantine was interested in supporting orthodoxy, which was why he call for the First Council of Nicaea to deal with the Arian heresy. As far as I know, or have been able to find Nicaea had no role in liturgical practice at all, in either East or West (except for prohibiting kneeling during the consecration on Sundays and during the Pentecost season, and excepting the fact that the Creed was recited at Mass.)
As far as the use of Latin is concerned it was the vernacular for most of the western world until at least the 8th century. This is at least three hundred years after Constantine and Nicaea. Certainly Medieval Latin served the same purpose during the High Middle Ages as French did in the post Renaissance period and that English does today. For example English is used as the international language of pilots and air traffic control, as well as in the Mass in many countries where only a small number of people speak the local dialect, and for which no vernacular translation of the Mass exists. ( I should acknowledged that both Spanish and French perform the same funtion in regard to liturgy in differnet parts of the world.)
The Mass itself , as a sacrificial ritual, predates Constantine. We have records from as long ago as the second century, some written by Pope Clement I, who likely was alive during the time St. Peter and St. Paul were in Rome. Even the Didache describes liturgical worship. I would remind you that this document was unavailable to Renaissance writers and though found in 1873 was mostly ignored by modern historians unitl after the discovery of the Dead Sea Scrolls. It's definitive origin in the late first century, contemporaneous with the Apostles and the early church was only widely accepted in the 1970s, after the changes in the liturgy which were implemented in the Post Vatican II era.
As for the use of Latin in the Mass this also pre-dated Constantine, probably dating from the middle of the third century. Pope Gregory the Great in the sixth century, hundreds of years after Constantine made a major revision of the way the Mass was said, which was in Latin, at that time the vernacular. There were still many regional variations at this time. Charles the Great (Charlemagne), who conquered much of Western Europe during his life ordered that the Mass according to the Roman rite (that is the Mass as celebrated in Rome) be said throughout his realm. By this time the Romance Languages were developing and Latin was a distinct separate language. Spoken by most of the nobility for sure and in most places the only language which actually had a written form. It would be a hundred years or more later before the Romance languages were written and several hundred years later before languages outside of Southern Europe developed their own written language.
I think you can see how something which was ritualistic, like liturgy, that had a rhythm and cycle of readings required a language that not only could be written but was also commonly read in an international sense. Don't forget that for much of this period concepts of French or Italian or German as a national identity did not exists. At the same time there were areas of Europe that did not use the Roman rite. Ireland for example had its own rite, the Celtic rite, which lasted into the 12the century. It was also said in Latin, which was obviously not a vernacular language for that country, but considering that Ireland was Christianize by St Patrick, who was a British Roman I guess that use of Latin should not be surprising.
The narrative of the pre-Vatican II Mass as a exclusionary ritual where by the priest mumbled in Latin while the faithful, ignorant of what was happening, prayed rosaries is mis-guided simplification. The Latin responses were learned by eight year olds. I can attest to you that I certainly knew what Et cum spiritu tuo meant when I intoned it. In Europe and America Latin was taught in every Catholic high school and even many secular ones. I can attest to the fact my father who never never finished high school, could recite the standard prayers in both Latin and English, knew the Tridentine Mass probably better than most modern faithful know the Novus Ordo, and as an adult the Liturgy responses he no doubt learned as a boy. I don't doubt there were people who could not do this and did not understand what was happening at Mass. I would also maintain that many of the modern faithful have mastery of English ( or Spanish or French...) have no idea of what is happening at Mass. Indeed at a certain level no one truly knows, it is a mystery of faith, something we cannot know this side of death. The fact that they understand the words without grasping their meaning, or in many cases misunderstanding their meaning is not an improvement of the situation.
My last point is that the demonizing of Constantine by sources inside the Church as opposed to Protestants outside the Church is a something which has its roots in the mid twentieth century modernist movement. This is the same movement which used Vatican II's valid and specific documents as an excuse to do many things never called for by the council, one of which was the elimination of Latin as a liturgical language. The Vatican II document Sancrosanctum Concilium actually called for Latin to be retained in the Liturgy and required that the faithful (that's us) know all of the Propers of the Mass in Latin. It says:
1. Particular law remaining in force, the use of the Latin language is to be preserved in the Latin rites.2. But since the use of the mother tongue, whether in the Mass, the administration of the sacraments, or other parts of the liturgy, frequently may be of great advantage to the people, the limits of its employment may be extended. This will apply in the first place to the readings and directives, and to some of the prayers and chants, according to the regulations on this matter to be laid down separately in subsequent chapters.
As can be seen Vatican II called for the retention of Latin in the Mass. Whether its elimination is good or not is another discussion. But whether good or not its elimination was not called for by the council. Books written by people in the group who implemented that change admit that it was an action taken to make the Mass more appealing to Protestants, not an action to either improve the quality of Liturgical Worship nor to edify the sacrifice which is taking place therein.
At many places the sacrificial character of the Mass has been completely subsumed in a paradigm of communal meal, so much so that a good portion of the faithful in those places no longer believe in the Real Presence.
I have been very fortunate at my parish to always have a priest who is faithful to spirit of the liturgical celebration, and one who follows the rubrics and forms of the liturgical worship. Not every parish has been so fortunate, resulting in large numbers of faithful who are more ignorant what is happening at the Liturgy than ever existed when the Mass was said in Latin.