I grew up in the Roman Catholic Church, I completed all the sacraments, because our parish Bishop told us that there is no other way to enter heaven, except through keeping the sacraments in the the Mother Church. The Bishop told us that Jesus gave the Apostle Peter (the first Pope of Rome) the keys to heaven.
One of my best friends grew up in the Greek Orthodox Church, where He was taught that there is no salvation outside of the Greek Orthodox Church. He said the Patriarch told them that Jesus chose to leave His final message with the Greeks, in the isle of Patmos and that's true. The Apostle John did receive the final message in Greece.
Every denomination adds their requirements to the gospel, each creates a unique set of requirements for their congregation to follow. These requirements are given as a condition to receive salvation, some denominations add around 20 requirements to the gospel and others add 509
Every denomination choses their own unique requirements, that way the congregation is trapped and most in the congregation believe they will lose their salvation if they join a different denomination. They even call people who leave traitors and their family and friends despise them, so the denominations wield a lot of power over their congregation.
My Priest told me that the biggest mistake the Vatican ever made was to release the bible to the public. He said, if you give 10 people a bible and ask them to read it, they would come back with 10 different interpretations and that's the undeniable truth. Allowing the public to own a bible has resulted in the disintegrating of the Church and 45,000 Christian Sects, Cults and Denominations.
The truth is you can make the bible say whatever you want it to say, as evidenced by the 45,000 denominations. It's wishful thinking to say there are only 3 gospels, because everyone adds their own spin to the gospel message. My Priest gave me a book, which had all the main Denominations and what they believe. I was shocked to find the large number of radically different gospels and doctrines.
I have since lost the book and I haven't been able to find another copy because I don't even remember the exact title as it was given to me 16 years ago. But the tile was something like "finding your way to the true religion", anyway it was certainly shocking.
I don't share your view that anybody can interpret the bible correctly if they just read it. If that was true we wouldn't have 45,000 opposing Denominations.