Although Volf argues that Christians and Muslims worship the same God and difference only comes in the way in which the religions worship, Scot McKnight, a theologian at Northern Baptist Theological Seminary in Illinois, argues that while both religions are monotheistic, only Christians believe in a God that has taken on human form and is also revealed in the Holy Trinity.
"I have said this before and will say it again: we can agree to some degree at a generic level, but we don't worship God in the generic," McKnight wrote. "We worship either the God of Abraham and Moses, the God of our Lord Jesus Christ, or the God of Muhammed. The God in each of the faiths is understood differently enough to conclude that saying we worship the 'same' God muddies the water."
While McKnight and others argue that Christians and Muslims can't be worshipping the same God because Muslims don't believe in the Trinity, Francis Beckwith, a professor at Baylor University, wrote that just because Muslims don't believe in the Holy Trinity doesn't mean that they aren't worshipping the same God.
Beckwith provided an analogy as an example.
"Imagine that Fred believes that the evidence is convincing that Thomas Jefferson (TJ) sired several children with his slave Sally Hemings (SH), and thus Fred believes that TJ has the property of 'being a father to several of SH's children.' On the other hand, suppose Bob does not find the evidence convincing and thus believes that TJ does not have the property of 'being a father to several of SH's children,'" Beckwith wrote. "Would it follow from this that Fred and Bob do not believe that the third president of the United States was the same man?"
"Of course not. In the same way, Abraham and Moses did not believe that God is a Trinity, but St. Augustine, St. Thomas Aquinas, and Billy Graham do," Beckwith continued. "Does that mean that Augustine, Aquinas, and Graham do not worship the same God as Abraham and Moses? Again, of course not. The fact that one may have incomplete knowledge or hold a false belief about another person — whether human or divine — does not mean that someone who has better or truer knowledge about that person is not thinking about the same person."
In his Washington Post op-ed, Volf argued that it is hypocritical for Christians to believe that they worship the same god as the Jews do but for them to detest the notion that Christians worship the same God as Muslims.
"Why is the Christian response to Muslim denial of the Trinity and the incarnation not the same as the response to similar Jewish denial?" Volf asked. "Many Christians today see themselves at war with the Islamic State and, by a deeply problematic extension, with the Islam itself. War, like enmity in general, requires clear and hard boundaries. We define our enemies as what we are not; we take any blurring of those boundaries as a threat to the legitimacy of our enmity."