Here's a mini history lesson
Y there's so many denominations:
Christians were heavily persecuted during the early years of the church from the apostles' time to about 315 AD. About that time, the Roman Emporer Constantine(who was a pagan, later turned christian and baptized in 337) legalized Christianity, formed the orthodoxy, and chose which books went into the Bible. He was presented with 80 books of the Bible and only chose to put in the books that referred directly to Jesus's teachings.....all other books were banned as heresy. Also, it's interesting to note that yes the sabbath day is normally referred to sunday-the 7th day but at the time they named sunday the sabboth day because sunday was the pagans day to worship their sun god.
A few years later, another Roman Emporer made Christianity mandatory throughout the Roman Empire. Some people might expect this to have been a positive development for the cause of Christianity, but actually it was disastrous. Any knowledgable Christian is well aware that no one can make anyone else become a Christian. It is impossible to force anyone to believe something in their heart. Only God can open hearts.
So instead of making Christians out of everyone in the Roman Empire, the decree from the emperor simply resulted in all of the religions in the empire mixing together as one and calling themselves "Christian". Those who followed Christianity, those who followed Judaism, and those who followed any one of the many different Pagan religions were now suddenly all in the same assembly. Even though the church was said to be "Christian", only a minority of the members actually were Christians. Most of the church members were of some other religion the day before, but were now calling themselves "Christians". The doctrines of these many religions were combined, resulting in a "church" whose doctrine was part Christian, part Jewish, and part Pagan. This was the origin of the Catholic Church.
As one might expect, a church that is a blend of multiple religions would not have doctrine consistant with the Bible, despite having a state mandated Christian label. Those who looked to the Bible for guidance quickly found that the church was not in line with the scriptures. To fix this problem, the clergy declared that only they could interpret the scriptures and that the church members should stop reading the Bible. The Bible became contraband and during the dark ages from about 500 AD to about 1500 AD, the public was not permitted to have access to the Bible. Only the clergy could look upon the Word of God.
They then dispensed only tiny morsels to the masses, often twisting the meaning for their own financial or political gain. By the time the reformation began, virtually all Biblical truth had been lost or distorted. Finally around 1500-1600 AD, the reformers began to get Bibles back into the hands of the common man. Right away, people began to protest against some of the Catholic doctrines and tried to reconstruct the proper church doctrines which had been lost more than one thousand years before.
Of course this was very difficult because they had been steeped in all manner of real heresies for centuries. Different groups had varying degrees of success, correcting some areas of doctrine while failing to correct others. Some false doctrines were changed into new, different false doctrines. Despite all the doctrinal corrections that the many denominations made, not one of the hundreds of denominations or sects ever made it back to the pure doctrine of the early church. Perhaps I should not use the word "pure", since we can see from Galatians 3 and 1 Corinthians 5 that errant doctrine was creeping into some local churches even at that early date. There is a quote that I have heard many times, and I am not sure who first said it: "The only problem with the protestants is that they did not protest enough." Therefore, we must be diligent in studying God's Word to know His true will, rather than relying upon any denomination to tell us.
Also, interesting trivia - In 336, before the emporer bacame a christian- Christmas was first celebrated on December 25th. This is the same date as the first-century BCE Roman holiday for the sun god Mithra.
Thought someone may find this interesting