I believe there is only one God, and that all the monotheistic religions believe in that same one God, though they may call him by different names -- Yahweh, Jehovah, Allah, Vāhigurū (the latter is the one personal and transcendent creator god of Sikhism). And they all may believe in or experience different attributes of God. Our human minds are limited, so we can only comprehend a small fraction of what God is like. It would stand to reason that different peoples over time in attempting to understand God as he has revealed himself to them have described him in different ways, like the blind men describing the elephant (one says it's like a rope, because he is feeling the tail; one says it's like a tree trunk, because he is feeling one of the legs, etc.).
We in the Judeo-Christian tradition believe that God has revealed something of himself to us through Scripture (though certainly not all of himself; even all the books in the whole earth couldn't contain all there is to know about God). Christians also believe that God's ultimate self-revelation was through his Son, Jesus Christ. While they do put us in somewhat of a unique position with respect to understanding "which God" there is, these things don't exempt us from the same limiting factors that all people of various faiths are bound by, namely finite minds further clouded by sin. We are like the blind men with the elephant when we read Scripture. Some of us (Christians) see great prophetic passages in the Old Testament (or "First Testament" as some Christians choose to call it so as not to offend Jews) and perceive that those texts are surely talking about Jesus of Nazareth. Others of us (of the Jewish faith) see the prophetic texts -- e.g., about the Suffering Servant -- as referring to the nation of Israel. So who is right? Or are we both right in some sense? I think we both need each other for a full understanding and interpretation of Scripture. And perhaps we Jews and Christians also need devout Muslims and Sikhs and others to elucidate other aspects of God that our sacred texts and traditions might not have taught us about. And likewise Muslims and Sikhs need us to tell them what we've learned about the good news of redemption through Christ, among other things. I think it is arrogant of any of us to say we have "the truth, the whole truth, and nothing but the truth, so help me God." Even if Christians do have a corner on the truth (which I don't think we do), it certainly won't win us any hearing with others to go about claiming that they are wrong and need to believe the way we do.
At this stage in my life, I am coming to a place of trying to live well within a pluralistic society. I have seen too much hatred and war between people of different religions to think that vigorously defending our differences is worth it. I'd rather look first for our common ground and engage in respectful dialogue about our differences from there. While I expect to go to my grave still believing in Christ as Lord, and the Bible as the Word of God, I still want to learn from my neighbors of other religious traditions rather than view them as "projects" to work on (those Christian tracts about how to witness to Jehovah's Witnesses or Muslims or Mormons used to intrigue me, but now make me cringe). My church upbringing taught me how to interpret Christ's statement of being "the Way, the Truth, and the Life," the One through whom "no one comes to the Father" without. But I'm open to the possibility that our interpretation might not be 100% correct. Are there not others who can relate to God as Father without knowing Christ? Or perhaps it is through Christ that they are enabled to come to God, even though they are not aware of his mediatorial role. (See Romans 2.) I'm more inclined to believe the latter.
I had some neighbors across the street from me who were Sikhs and were very friendly. They were pretty assimilated into American culture and didn't wear the turban or kirpan, but their relatives who visited them from time to time (and to whom they introduced me) did. My pleasant encounter with these Sikh neighbors has given me a curiosity about the Sikh religion. It was fascinating to read some of the stories about its founder Guru Nanak and find them quite similar to stories about Jesus in the Christian Bible. It made me wonder whether Guru Nanak might have been Christ in the flesh again. Jesus rose from the dead and is at the right hand of the Father, but who says he cannot appear in our presence again (as he did with the disciples after his resurrection) and perhaps even be unrecognized as the incarnate God again (as he was on the Road to Emmaus)?
I found a very good articulation by Diana L. Eck of what I think is a good way of relating to those of other faiths. Worth quoting in its entirety here:
"The plurality of religious traditions and cultures has come to characterize every part of the world today. But what is pluralism? Here are four points to begin our thinking:
• First, pluralism is not diversity alone, but the energetic engagement with diversity. Diversity can and has meant the creation of religious ghettoes with little traffic between or among them. Today, religious diversity is a given, but pluralism is not a given; it is an achievement. Mere diversity without real encounter and relationship will yield increasing tensions in our societies.
• Second, pluralism is not just tolerance, but the active seeking of understanding across lines of difference. Tolerance is a necessary public virtue, but it does not require Christians and Muslims, Hindus, Jews, and ardent secularists to know anything about one another. Tolerance is too thin a foundation for a world of religious difference and proximity. It does nothing to remove our ignorance of one another, and leaves in place the stereotype, the half-truth, the fears that underlie old patterns of division and violence. In the world in which we live today, our ignorance of one another will be increasingly costly.
• Third, pluralism is not relativism, but the encounter of commitments. The new paradigm of pluralism does not require us to leave our identities and our commitments behind, for pluralism is the encounter of commitments. It means holding our deepest differences, even our religious differences, not in isolation, but in relationship to one another.
• Fourth, pluralism is based on dialogue. The language of pluralism is that of dialogue and encounter, give and take, criticism and self-criticism. Dialogue means both speaking and listening, and that process reveals both common understandings and real differences. Dialogue does not mean everyone at the “table” will agree with one another. Pluralism involves the commitment to being at the table -- with one’s commitments."