First of all, I hope that it is clear that this project had nothing to do with "watering down" theology. Most of the time, when people talk about taking theological ideas metaphorically, they mean that they don't really believe it. If someone says that they believe "God is a metaphor" (i.e. for the sacredness of the world, or compassion for the needy, or whatever), that means that they don't really believe in God; they're actually atheists cloaking themselves in religious language.
On the other hand, if there really is a Creator of infinite power and wisdom who designed the Universe, it makes sense that he would be beyond our capability to grasp. We can say what God is not, but we cannot understand him in any positive way except by making metaphors. Precisely because we Christians believe that God exists, we have to resort to metaphors in order to describe him.
You may have noticed that many of the metaphors I pointed out in the Creed are actually ordinary figures of speech which are used all the time by regular speakers. While others are attempting to describe aspects of the Divine Nature, which transcends all understanding. I make no apology for including both of these together. Metaphors are practical as well as mystical. The human mind is an incorrigable metaphor-machine, and we pretty much resort to metaphors all the time, even for understanding things which are closer to earth than God. Yes, Theology is metaphorical—but then again so is everything else.
Perhaps this is another way in which we humans are created in the "image of God". Even God the Father, it seems, uses a metaphor to understand himself: his self-understanding is the Word (the rationality, intelligence, self-expresssion) of God which is coeternal with him. It turns out though, that the Son is a quite excellent metaphor for representing the Father, since he is exactly like him in every respect. (Hint: this paragraph contains another metaphor).
Now, let me draw out some implications for how we do Theology. Atheists love to point out that the biblical description of God is full of contradictions. This is, of course, quite true and a natural consequence of the fact that we understand God through metaphors. That is, we say that God is like a Father, or like a Judge, etc. God is unchanging, and yet he changes his mind when we intercede for others. He cannot be contained in the highest heavens, yet he tells Jesus to sit at his right hand. All things are possible for him, yet it is impossible for him to lie. He dwells in impenetrable darkness, and yet in him there is no darkness at all.
If the metaphors contradict each other, that doesn't mean that the reality is self-contradictory. It just means that the images conflict, if you take them literally. But you aren't supposed to take them all literally. Paradox is a way of seeing the invisible. You can see in three dimensions precisely because the image in your left eye doesn't quite agree with the image in your right eye.
(This should be enough to show why we Christians don't have to literally believe that 1 = 3. It's fun to express things in a paradoxical way, but here we've helped you out a little by inventing some vocabulary. The thing that God is one of is called, in technical language his substance or essence. The thing that he is three of is called persons or hypostases. 1 substance = 3 persons is not actually a logical contradiction.)
You might wonder what ties all of this speculation down. How do we know our metaphors correspond to an actual objective reality? The answer is simple. Metaphors about the beauty of nature, or social justice, cannot turn water into wine, or raise the dead. In the end, Theology is about selecting the most reasonable theories which explain the sense-data of certain human beings. Just like, you know, Science.
But if we can't recognize the metaphors in Theology, then of course we will end up thinking it is superstitious and ignorant and cannot be reconciled with Science.
Rationalists like to tell a narrative something like this: "The ancients were ignorant and made up a bunch of mythology which they took literally, but now we know that it contradicts Science™. Sensible atheists like ourselves reject this mythology, while the more sensible among religious people manage to hold onto it, by reinterpreting most of it to be metaphors. Yet if people had known about Science™ from the beginning, they never would have believed in God or heaven or angels or any of that." As if the culture which gave us the Song of Solomon was incapable of understanding the idea of metaphor!
Many of the images, taken literally, would indeed be silly. For example, the Bible is full of body-language descriptions of God, yet no serious Christian theologian has ever thought that the Father has a body. That's because the ability to use and recognize metaphors didn't come down from Heaven to Earth during the Age of Enlightenment. It has always been with us, as long as there have been human beings. So if we don't watch it, people might even use metaphors to descibe scientific theories!
Of course, even if people did mistakenly believe something to be literal, that doesn't necessarily mean that the core idea is eliminated by reinterpreting some of the details as being metaphorical. (There's a good discussion about this in St. Lewis' book on Miracles.)
As a specific example, there is one example of something I think is a metaphor in the Nicene Creed, which historically at least some Christians have taken literally, although almost no one would nowadays. I refer to Heaven being literally up, somewhere among or outside the planets or stars. This is most famously illustrated in St. Dante's Paradiso, in which the blessed in heaven are assigned positions associated with the various planets. Dante himself was certainly aware of the allegory in his own poem, but I assume he was illustrating a common conception. Arguably, then, this is an exception to my statement that the metaphors in the Creed "would have been understood by educated ancient people".
So let's suppose that the Apostles, when they witnessed Jesus' Ascension, literally believed that Heaven is above the Earth. What of it? Either they actually saw what looked like Jesus going into the sky or they didn't. If they didn't see it, then Christian theology is just wrong, apart from any considerations involving Science. If they did see it, we still need to explain it somehow, even if we understand it using different imagery than the Apostles did. Although, since our own image of going to another universe would probably be just as metaphorical as theirs, maybe we should just stick with their metaphor, once we recognize that it is a metaphor. It was, after all, the metaphor Jesus was using, to communicate something about where he was going.
I'm not trying to say that all of the tensions between Science and Religion instantly disappear, once we recognize the existence of metaphors. There are substantive issues to discuss. But we won't be able to discuss them, if we can't distinguish the symbolism from the claims about reality.