Sometime before I started seminary I started wondering how to define whether or not someone believes in the God of the Bible. I think this question was on my mind in large part because of the efforts of liberal wings of Christianity, Judaism, and Islam to unite together in worship following 9/11. If I recall correctly, President Bush even gave a speech around that time in which he declared outright that Christians and Muslims worship the same God (or is it "god" with a little g?). Not only that, but the US government has granted millions of dollars to religious institutions like Fuller Theological Seminary to do research that might prove that Muslims, Christians, and Jews all believe in the same God.
Out of all this came a quest on my part to determine exact rules for knowing when the god in question is and is not the God of the Bible. This quest lasted for a couple of years and fizzled out with little success. Most who argue that God and Allah are not the same being cite the differences in their character, i.e. Allah is cold and impersonal and God is not. The problem with this understanding is that its logical conclusion would be that any two Christians who believe something different about God's character would then be serving two different gods, no matter how small the difference. For example, one who believes that God double-predestines would be serving a different God than the person who believes He only single-predestines. This logic troubled me, so I asked one of my theology professors how far one has to veer in his belief about God before he starts believing in a different god altogether. His answer was, "How much hair do you have to lose before you're bald?" This was not helpful.
I hadn't thought much about this question again until Saturday morning, when two Jehovah's Witnesses interrupted my efforts to fry some bacon by knocking on my front door and trying to convert my wife. I came to her rescue and ended up talking to the two men for nearly half an hour. They went around and around trying to tell me that Jesus was not God but a created being. I got out my Greek New Testament and showed them that Jesus really is God, which I don't think they expected from someone who lives on a gravel road (many thanks to Southern Seminary). I showed them from Scripture that God is three-in-one: Father, Son, and Holy Spirit. They weren't ready to submit themselves to what the Bible says, but one of them stayed quiet and seemed to be listening carefully, so there may be hope. The lesson that I learned from them came at the end when I asked them if I could pray for them. Their answer was no. They said that if I wanted to pray for them on my own then that's my business, but that they wouldn't bow down with me as I prayed to my "Trinity God." The funny thing is that without giving any thought to the issue of the previous paragraphs, I had already decided that I would not let them pray for me either if they asked. We both stood there and agreed that their god is not the same as my God, and then we parted ways.
The lesson that I learned from the Jehovah's Witnesses was that any god that is not the Trinity of Father, Son, and Holy Spirit is not the God of Christianity. While it's true that Christians, Muslims, and Jews all claim to worship the God of Abraham, it is also true that the God of Abraham has now shown us that He is three-in-one. Anyone who rejects the deity of Christ and the Holy Spirit serves a different god than the God of the Bible. This makes a lot of sense in light of 1 Peter 1:21, which says, "Through him [Jesus] you believe in God." This solves the question of whether other religions might be trying to worship the same God as us. For example, I feel confident in saying that the Jewish religion of today does not try to worship the right God in the wrong way, but that it serves a different god altogether from the one it served in the days of Moses. My confidence in this statement comes in their rejection of Jesus and the Holy Spirit as God.
The Jehovah's Witnesses didn't solve all my problems, though. I am still not sure where to draw the line within Trinitarian Christian faith when someone's idea of God seems far from what the Bible tells us. For example, I am not sure whether open theists (those who claim God does not know the future) worship a different god. To be fair to my theology professor, this is probably the kind of situation he was thinking of when he made the bald joke. Maybe someday God will help someone figure this out definitively and they can let me know. If that's you, then please comment.