In discussing the question “Do Muslims and Christians worship the same God?”, I personally like to use the example of the way two different people, a progressive and a traditionalist, may talk about (just for eg.) the Catholic Archbishop of Brisbane. They may claim to be talking about the same person, but by the way they describe that person (from their point of view) they might well be talking about two completely different people.
Suppose that you and I both knew millionaire Bruce Wayne. I might know, because he revealed it to me, that he is also Batman. You may hear this claim and reject it, in which case you adopt the false corollary belief “Batman is not Bruce Wayne.” That does not mean that you don’t know and relate to either Bruce or Batman, it means only that you misunderstand the relationship between them.
In the same way, one may worship God and honor Jesus as a prophet (which he was) without understanding that Jesus is God. Indeed, many people in his own day did that: They knew the historical Jesus but had a false understanding of his identity.
Not only does this apply to Christain and Muslim disagreement over the identity of Jesus, but it also applies to the question about whether or not God is Triune or radically Monadic. And here comes the question of knowledge on the basis of reason and knowledge on the basis of revelation.
I cannot deduce that Bruce Wayne is Batman from reason alone. Yet although I cannot know that Bruce Wayne is Batman without this fact being revealed to me, nevertheless this fact cannot be said to be against reason, precisely because Bruce Wayne really IS Batman. Just so, I cannot know that God is Triune from the use of reason alone–such knowledge requires revelation. But given the truth that God’s nature is Triune, it cannot be said to be against reason, because that is the reality.
Moreover, you and I both know Bruce Wayne. But you think he is a playboy millionaire and I know (from revelation) that he is Batman. We both know the same man, but we have radically different ideas about his true identity. Nevertheless, your understanding of him is not unreasonable, given the limits of your knowledge. Even if I tell you “Bruce Wayne is Batman”, it would not be unreasonable for you to disbelieve me, because (on the basis of your experience) Bruce Wayne is a playboy millionaire.
I think you can really go somewhere with this example. Perhaps even further than using the example of the Archbishop of Brisbane. Unless, of course, HE is Batman. Now there’s a thought…