If Jews, Muslims and Christians all believe in “the God of Abraham” . . . why would it be said that these religions believe in different gods? How is that possible? Is it not the same/only God but people themselves who possess very different (even incorrect) understandings of who God is and what He did (come as Jesus/remit sins)?
Well, a few things first. If you simply read the Quran the god described in it is clearly not the God of the Bible. Many books, articles, even blogs can demonstrate this easily. Second, while Jews do read the OT they also have the distortions from Judaism found in extra-biblical sources such as the Talmud. There are dangers in reading these things uncritically because they do not approach the OT like Jesus and the Apostles did. Also, our God was robed in flesh. Jews resist this truth and Paul even says Judaism in his day was the domain of principalities and powers (see Gal. 4:3, 9 and Col. 2:8, 20). We see the claim Judaism was under control of principalities and powers is further verified true in that they even crucified their Messiah, our Lord. The differences then are not merely incidental but are critical because ultimately it’s not simply the intellectual inconsistencies but in reality the difference in Lordship. One is of God; the other is ruled by demonic forces.
However, after all of this is said, sincere prayer is promised something. That the Spirit of God will lead and guide you to ALL, not some, truth. People can be sincere. But they are still sincerely wrong and still lost. But the promise is the hungry, the sincere, as long as they continue to be led, will find a God who loves enough to guide to ALL truth. Many do come from other faiths. Still many others find separation from tradition, family or the familiar too much to give up. But remember the constant is God’s call, and God calls all people to all truth.
I am not saying it’s the best witnessing technique to say, “Your religion is the domain of principalities and powers…” I’m pointing out here the Scripture teaches sincere people open themselves up to manipulation by deception. So attempting to minimize differences does not help us evangelize people. We must win those that “oppose themselves” by calling them to “repentance to the acknowledging of the truth” (2 Tim. 2:25). I will also add that sincerity matters in keeping truth, too. If people raised in truth don’t love it as much as those that hunger enough to find it, they will lose it. This explains why some never seem to find it and why some leave it.