John Mark Reynolds, 2004.
I am sometimes asked how I know my God is the true God. How do I know the Aztec god or the gods of Olympus are not real gods?Here is a short (blog length!) response. People curious about more information should read Scaling the Secular City.
First, we must ask ourselves what was claimed about the god in question. If we take Zeus as an example, we can see that beyond his anthropomorphic features and “deathlessness,” there was not much more to him. The criticisms of Heraclitus and others seem appropriate. Zeus is just a glorified human being. If cows had gods, they would create a cow-like god. There is nothing interesting philosophically about Zeus. Most other gods in polytheistic systems fit this model. When Zeus began to be transformed by the philosophers (Heraclitus and Plato especially), Zeus began to look more and more like the God of the Jews and Christians.
Notice that I am not questioning the religious experience of polytheists. For all I know they had real contact with the supernatural realm. In fact, it seems reasonable to believe that something interesting was happening at Delphi. The question is what to make of it. The god of Delphi does not seem worthy of worship, he is too small and parochial. This is not just a matter of “my god can bench press more universes that yours,” but of intellectual interest. A god that is all-knowing is more interesting, better, than a god who knows only the affairs of his little people. For all I know, they worshipped demons at Delphi. It does not matter for their god is too small to be worthy of worship even if he is good.
Of course, the God of the Old Testament is sometimes given human characteristics to communicate to people. (“The arm/eye/hand of the Lord”) However, Scripture makes it clear that these are “ways of speaking” in a way that Homer and Hesiod never do. Zeus is just a super-man who is deathless, God is something totally other by the end of the Old Testament revelation. The same process led the Greeks to a god much more like the God of the Bible than Zeus (though they retained the name.) Plato and the Jews had more in common than Plato and Homer. This god of the philosophers is enough like the God of the Bible that I think we can identify the two. The same thing is true of the great monotheistic traditions. There are important differences (often vitally important) between attributes of god postulated in Islam, Judaism, and Christianity. Still, they have enough in common to point to what would have to be the same being: all powerful in nature, all knowing, present in all places.
There cannot be (logically) two all-powerful beings. So I would argue that the god of the great monotheistic religions is worthy of belief for basically the same reasons. (See arguments for the existence of God in William Lane Craig and JP Moreland.) In short, philosophy can carry one pretty far forward to what kind of God there would be (more like Aristotle less like Hesiod). It also can show what kind of God would not be worthy of worship…such as a god who did morally evil things (see Zeus again). The second thing to do is to examine the major claims of Christianity about the god of the philosophers and see if those work. This would include issues like the incarnation and Trinitarian theology.