I guess the question is, how do you know when you've found one of the universal truths? How do you distinguish those from anything else you perceive?
Funny you should ask.
This is the reason why we have prophets actually. Their job is to teach you the universal truths. Each prophet talks about the "same" set of universal truths, but each new one had more information than the previous. Not different, but more in depth information. Mohammed is considered better than the previous ones not because he delivered a different message, but the same message in more depth.
So, you read the Quran, the bible etc and instead of reading them like a history book or a book of facts, you try to get into the mindset of the people and events mentioned and extract the mindset you should have in your own mind.
Contrary to the common understanding, these books are filled with symbolism. Things are rarely literally the way they are written.. For example, when the Quran says "Heaven has rivers of milk and wine and honey", this is pure symbolism... Also keep in mind that some words have multiple meanings. When Quran talks about heaven and earth, these not only literally mean the sky and the land, but they also mean the body and the mind. Furthermore, some conversations -for example between God and the angels- are there so that you can grasp it. Not because God literally talked to the angels.
If you read carefully, these books depict all the situations you'll ever encounter in your lifetime and they tell you what your mindset should be towards each circumstance. Of course if you read them literally, then you'll dress up the way people did two thousand years ago and act like them, but that won't get you anywhere.
As for the people who supposedly read these books and do horrible things (ex: kill in the name of God) based on the information in them, they clearly missed the meaning of the message! Every person can really only save himself. For the others, all you can do is point them in the right direction. Whether they follow it or not, is really up to themselves. But of course, people will use anything to control others and religion is a great leverage.