Common men could not read, period.
So men had to rely solely upon the priest to interpret the scriptures for them, which is by the way against the word itself.
Not true.
"And account the longsuffering of our Lord, salvation; as also our most dear brother Paul, according to the wisdom given him, hath written to you: As also in all his epistles, speaking in them of these things; in which are certain things hard to be understood, which the unlearned and unstable wrest, as they do also the other scriptures, to their own destruction. You therefore, brethren, knowing these things before, take heed, lest being led aside by the error of the unwise, you fall from your own steadfastness." 2 Peter 3:15-17
You haven't even begun to master the subject you attempt to tackle here. For starters, you complain that, when the Greek Scriptures were translated into the Latin Vulgate, it was a version "which common men could not read for themselves. So men had to rely soley upon the priest to interpret the scriptures for them, which is by the way against the word itself." You do not seem to be aware of the fact that "Vulgate" Latin IS the common-man version of that language. To the extent that common men could read at all, it was a *help*, not a hindrance, to every man in the western Roman EMpire that the Scriptures were so translated. To the extent that many common people were illiterate, yes, the priest DID have to read the Scriptures to them, but there was no "translation" necessary here, as the words were in the plain language of the people in the west, whom St. Jerome had in mind when he undertook the translation project in the first place.
Second, speaking of St. Jerome, your post seems to conflate his efforts with the rise of Constantine and the legitimation of Christianity in the Roman Empire. This is incorrect. St. Jerome translated the Vulgate between 380 and 405 AD. Constantine's Edict of Milan, legalizing Christianity, was promulgated in 313, well before St. Jerome was even born.
Third, the Jews did NOT canonize the Old Testament Scriptures until their Counci of Jamnia (sometimes written Javneh) in the 90's AD. This is not only NOT "long before the Catholic Church existed" as you say, but, indeed, the Council was held in large measure to counter early Christian (Catholic) claims about Scripture and salvation history. To the extent that this council was not convened until 60 years after the birth of the Church at Pentecost, and 20 years after the destruction of the Temple and the sacrificial priesthood of the Jews, one wonders why any Christian - Catholic or otherwise - would invest it with any kind of authority, as the Apostles and their successors had superseded Jewish authority long since. That the early Protestants retroactively invested this council with such legitimacy *precisely* to justify their alteration of the settled Christian OT and NT canon is most telling.
Meantime, the early Church had already settled on the Alexandrian version of the Old Testament in Greek by the early second century (at the latest), and had also largely settled on the New Testament canon by that century's end, when canonical NT writings had circulated well throughout the Church. From 382 to 419, various regional councils in the Church promulgated the New Testament canon we both share, as well as the 46-book Old Testament canon Catholics still embrace. The 39-book OT canon you have is only justified by the Council of Jamnia's decisions, already noted, whose pronouncements are of no notice to Christians, as that Council no longer had authority. Indeed, if consistency were to reign here, you would, on the basis of that Council's decisions, jettison the ENTIRE New Testament, as it specifically rejected all the books cntained therein!
On another recent post, you frankly admitted that you are largely self-taught in the Christian faith. Nothing wrong with that! But the sources you have used on which to base your learning are highly deficient, even in the basics. I urge you to dig deeper.
Correction: The Original Canon of Scripture was in Latin & Greek, which WAS the language of the common people. (350AD or so) You are thinking in terms of the Middle Ages. Your lack of Church History is not good.
WRONG. Anybody who could read, read Latin. It was the universal tongue of educated men, just as French used to be and English is becoming. The scriptures were sifted by learned men - the early Church fathers, some of whom knew the Apostles personally. Ancient tradition has it that Ignatius, Bishop of Antioch, was the child who sat in Jesus's lap at the Blessing of the Children -- and he and Polycarp were disciples of St. John.
Most "common men" couldn't read at all. Remember what Thomas Aquinas said in Adore devote, "faith comes by hearing" not by reading. It wasn't until the Reformation and primarily in England (which had an English-literate yeoman class by that time) that reading the scriptures for oneself became a battle cry.
You're also wrong about the Old Testament. In the Mediterranean region the LXX (Septuagint) was used by everyone, including Jesus who quotes from it several times. The Hebrew scriptures are a different canon, they don't contain all the same books.
Constantine didn't "convert" to Christianity.
He co-opted it and buried it for 1200 years.