All religions are valid paths to a transcendent Truth or divinity (capital "T" Truth means it's an ideal--unattainable and yet real at the same time). Christianity, Buddhism, Jainism, Hinduism, Judaism, and the Baha'i faith are all after the same thing. But across time, language, geography and history they find it in different ways. These different ways, beliefs and practices are philosophically compatible.
Wait a minute. Bull shit. Jesus is God. Muhammad is His only prophet. How are those compatible?
This is where Kant comes in (and John Hick's An Interpretation of Relgion). All of these "beliefs" are no more than beliefs; they are grasping at a transcendent world that we cannot reach, unverifiable speculations about the nuemenal realm; doctrine or dogma is not knowledge. Beliefs, by definition, can be wrong. Only knowledge can be truly incompatible with non-knowledge (error). Nobody can disagree with e=mc2. But "Jesus is God" is on the exact same epistemological level as "Muhammad is His only prophet." We simply don't know; thus we believe. Therefore, they are both equally valid ways of thinking about God. Because we will never know, they can both exist together just fine.
And that's okay.
Two people stand in front of a Van Gogh. It means this, one says. No, says the other, it means this! They both give reasons. Perhaps we should ask the artist? Well, he's dead--and would that even help? Thus we have two different meanings of a piece of art that are compatible and can exist together just fine.
When it comes to practice (ritual), religions are quite different. When it comes to metaphysical beliefs, quite different. That's to be expected. But when it comes to morals, very similar. The moral codes of the major world religions are all based on love, compassion, forgiveness. They are compatible. They ground virtue and suppress vice in amazing different ways. Sweep away the hypocracy and you are left with love as the bedrock of religion.
Pluralism is an expression of love for other people, yet this will not satisfy a lot of people. Religious Pluralism is not for people who get angry when other people talk about other beliefs. It's not for people who are offended by the existence of Islam, or who use religion to define what they are not (rather than what they are). It is not for dogmatic, intolerance, judgemental types. It's for people who love religion and take it seriously, who realize that they are Christian perhaps because they grew up in a Christian household or nation (and that's okay). It is for people who are humble, who have a lot to learn, who realize the transcendent nature of their beliefs and place their hope in them.