Religious pluralism, which I'll define as the view that all religions are equally true and valid, is for most people, deeply rooted in the idea that truth is relative. Truth is dependent upon a matter of perspective. This makes truth subjective and not objective, which makes it so one religion can't be exclusively correct. If I think Christianity is true, then it's true for me. If a Muslim believes the Qur'an's teachings are true, then it's true for that individual. Ultimately, this means everyone's religious view is true for the individual. I could not tell someone that their religious view is wrong.
Here's a problem with this line of thinking. Two plus two equals four. That's true a statement, and since it is true it is true for all people, at all times, and in all places. Even if I think two plus two equals five, and that's my perspective, I will be wrong because two plus two never equals five for anyone, anytime, anywhere. If it is true that Hu JinTao is president in China right now, then it's true for everyone, everywhere, in all situations. Truth, extends to everyone, and it is not changed on account of someone's personal view! This applies to religion!
Another example, I am a male! Regardless of your view or perspective, I am a man, and my wife is a woman.
Applying this principle, that truth extends to all, to religious pluralism, Jesus either is God (Christianity), or Jesus is not God (Judaism, Islam), or Jesus is one with the divine source that is at the heart of all things (Hinduism), or Jesus was just a dude (Buddhism).
Living Loud: Defending Your Faith contains a chapter entitled, "What is truth?", which speaks more in depth on this issue of relative truth. Click on the image of the book to get your copy of it today.