To those who feel it's impossible to believe that just one path to salvation is right & true when so many paths are out there, I ask you to consider this:
Imagine for a second that you would stop at nothing to ruin your enemy. Now imagine this enemy (we'll call him "Bob") has an extremely valuable one-of-a-kind painting that he needs to sell for a lot of money.
If your greatest goal in life is to ruin Bob, and you know about his painting, what would you do?
You might try to steal or ruin it. But let's assume Bob's no idiot, and has it perfectly protected. You can't get to it. Now what?
You do something you can control and Bob can't stop - you flood the market with counterfeits. And then you make sure that everybody knows about them.
You do this because you know the best way to devalue what is real is to make people question it's reality. And the best way to do that is to create numerous competitors. People must be forced to ask themselves, "How can I possibly know which is the real painting?!"
If they can't answer easily, most people won't buy any of them - while others will give up trying to figure it out and content themselves with a copy. Either way, the more they doubt the better.
That's why counterfeiting anything is such a serious crime. It undermines the value, power, and meaning of the real thing.
Now let's also assume that Satan's no dummy. As long as some people sincerely follow the wrong path and others in disgust refuse to believe anything at all, he wins.
That is at least one way to answer the questions: Why are there so many religions out there? And why should I believe just one?