Lest ye find yourself believing that one day the New Testament dropped from the heavens fully formed, and has been meticulously copied ever since, I'm sorry it is not so.
Much of what we know of as the new testament was first compiled together and commented on by Origen (185-254). Including Matthew, Mark, John, Luke, Acts and most of the letters. Though he also included many other books and letters which are no longer part of the New Testament. Based on his extensive reading of the literature at the time he believed in only one God, which was God the Father referred to by Yeshua. He also believed in reincarnation as a significant part of Yeshua's teachings.
Flavious Constantinus (272-337) was a Roman emperor (306-337) at a time where there was a great diversity of books floating around about the life of Yeshua. Unfortunately they were not following Yeshua's commandment to love and be kind to one another, and instead there was a great deal of infighting. Indeed most Romans worshipped a variety of humaniform gods, ranging from Apollo and Zeus to Julius Ceasar and Mithras. So Constantine organized the Council of Nicea to create a new God, which could be worshipped by the whole empire.
Constantine organized the Council of Nicea and invited Christians from around the empire.
When he asked gathered presbyters what the name of the new God would be, they could not agree, and held a ballot over a year and half, and made a short list of their top five: 1. Caesar 2. Krishna 3. Mithra 4. Horus 5. Zeus
Constantine decided there were too many factions with this, and so synthesized a new name for the new God they would be making. Since Constantine was of British origin he used the Druid God Hesus for a first name from the western end of the empire, and joined it with Krishna (Sanskrit for Christ) from the eastern end of the empire, in order to unify the East and West in one name. Thus Yeshua of Nazareth became Jesus Christ (source: Acta Concilii Nicaeni, 1618).
Consantine then decreed that the New Testament be compiled:
"Search ye these books, and whatever is good in them, that retain; but whatsoever is evil, that cast away. What is good in one book, unite ye with that which is good in another book. And whatsoever is thus brought together shall be called The Book of Books. And it shall be the doctrine of my people, which I will recommend unto all nations, that there shall be no more war for religions' sake."
(God's Book of Eskra, op. cit., chapter xlviii, paragraph 31)
Unfortunately during the heated debates that followed only made divisions worse between competing factions of Christians they focused not on what they had to follow in common (Jesus's commandments), but rather on which of their pet theories would become the dominant one (Monotheism vs Tritheism). In the end tritheism (trinity) won out, and the killing of Christians and burning of their scriptures by other Christians began in earnest with total disregard for Jesus's commandments.
"With his instructions fulfilled, Constantine then decreed that the New Testimonies would thereafter be called the "word of the Roman Savior God" (Life of Constantine, vol. iii, p. 29) and official to all presbyters sermonizing in the Roman Empire. He then ordered earlier presbyterial manuscripts and the records of the council "burnt" and declared that "any man found concealing writings should be stricken off from his shoulders" (beheaded) (ibid.). As the record shows, presbyterial writings previous to the Council of Nicaea no longer exist, except for some fragments that have survived."https://www.bibliotecapleyades.net/biblianazar/esp_biblianazar_40.htm
Interesting to note that of the few fragments we have of Matthew we have from before the great burning of scriptures began, there is no mention of Jesus being sovereign over all the earth or a trinity (Matt 28:18-19 respectively).
You know who was sovereign over the Heaven and the Earth at the time of the coucil? Ceasar.. Guess they did a little combining over there.
In the early ones of Matt 28:18 Jesus said ""just as my Father has sent me I am also sending you."" And Matt 28:19 is completely missing.https://www.biblequery.org/mtmss.html
So what do they say he was sending them for?
Matt 28:20 teach them to observe all, whatever I did command you, and lo, I am with you all the days -- till the full end of the age.'
And that my friends is how the new testament was formed, to the best of my understanding. There was a period of time of a couple centuries where people were allowed to own this New Testament. Until Emperor Justinian came on the scene and decided he wanted to change the interpretation of the scripture to exclude reincarnation. So after the 500's again the bibles were burned along with their owners, until the invention of the printing press made it infeasible in the 1500's. In fact it was still illegal to own a bible in Italy until 1870 ( https://romecorruptedchristianity.wordpress.com/2013/07/02/a-time-when-the-bible-was-banned-and-burned/
So yeah modern bible-based Christianity or protestantism is a fairly "new religion".
The new testament as ordained by Flavious Constantine, and compiled by the squabiling presbyters of Nicea, has passed down fairly in tact.
But of course you can consider that perhaps God had ordained it all, modifications and burnings included. Though certainly the burning and killing is against the commands of Yeshua/Jesus .
Personally it does not matter to me if you believe in the three gods of the trinity, or also add in a fourth god "satan/devil", or whether or not you deny reincarnation, or any other trivial point.
As far as I know, as long as you open your heart to God and follow Jesus's commandments (i.e. cultivate forgiveness, compassion and unconditional love for All beings including yourself) you'll attain the salvation of life age during.
I would like to remind you that we are not at liberty to judge whether anyone else will or will not achieve salvation, as God is the judge, not you. So my understanding of salvation is by faith alone.
Personally I follow Yeshua of Nazareth, and thus bypass the Constantine's Testament as a single authority, since indeed there are many many books not authorized by the squabbling council of Nicea which can be used to corroborate Yeshua's life.
From all I have read, the most important thing is to follow Jesus's commandments, forgive, love and be kind to one another.
Young's Literal Translation
34 `A new commandment I give to you, that ye love one another; according as I did love you, that ye also love one another;
35 in this shall all know that ye are my disciples, if ye may have love one to another.'
This commandment I give my stamp of approval as authentic.
I have some pre dawn prayers to perform so will end here.
May you be blessed.