Occasionally controversy arises as to whether Christians and Muslims worship “the same God.” (See here for an example.) I don’t find this to be a particularly helpful way of putting the issue: presumably there is, at most, one God, so asking whether two groups of people worship the “same God” must be shorthand for something else. With all due respect to polytheism, it’s not like there are multiple gods and the question is which god one’s worship is directed at.
What I think is really being asked is to what extent the two religions understand God in the same way. For example, Muslims deny the doctrines of the Incarnation and Trinity as Christians understand them. This doesn’t mean that there are two different “gods” but rather two different understandings of what the one God who exists is like. The object of the understanding is the same, but the manner in which that object is understood differs.
So given this difference, what should Christians’ attitude toward Muslims be? Should they be trying to convert them to (what Christians believe to be) a better understanding of God? Do Christians think that a person’s worship can only be “true” or that they can only be saved if they have a flawless understanding of God? That seems to be setting the bar too high. To be specific, do Christians deny that someone can worship God if one denies the Incarnation and the Trinity? Well, that would mean that all Jews, including most of the great figures of the Bible, worship a “false god.” It would also go against a longstanding Christian tradition that “virtuous pagans” could attain true (if incomplete) knowledge of God. Moreover, the Bible suggests that knowledge of God is available to all people–often outsiders to Israel’s history are depicted as worshiping God, and Paul notes that God’s existence and wisdom are evident to the Gentiles. Not to mention that Christians have long recognized that God exceeds the grasp of our understanding. So even if Christians believe they have a “truer” or more complete understanding of God than non-Christians, they should acknowledge that God transcends their comprehension. There thus seems to be no good reason to deny that Muslims are acquainted with God and worship God according to their lights.
What Christians should focus on, I think, is confessing the revelation they believe they have received. As the Anglican bishop John V. Taylor once said, for Christians, “whatever else he is, God is Christlike–humble and vulnerable in his love.” That is the central truth Christians are called to witness to. In their dialogue with people of other traditions, Christians should–humbly and vulnerably!–uphold this insight. It may be that other traditions obscure or even deny this insight; but it may equally be possible that adherents of other traditions can absorb this insight without abandoning their tradition. The goal shouldn’t be for everyone to “become Christian” but for everyone to hear and respond to the gospel of God’s unlimited love.