Theologians often claim that the nature of God is so far beyond our understanding that he must be completely unknowable to our finite, mortal minds. We must therefore approach describing him indirectly through metaphor, symbols and figures of speech. These are applied to God as rough and ready approximations. The best we can do is point to his unknowable nature using inevitably inadequate comparisons with what we do know.
A metaphor is a way of explaining or illuminating something unfamiliar by comparing it with something with which we are more familiar. The whole of human language is suffused with metaphors and could not operate without them. However, for a metaphor to work the creator of the metaphor has to have to have direct access to both parts -- the familiar bit, to which we make the comparison, and the unfamiliar bit which we are trying to illuminate by means of the comparison. If you don't have access to both parts then you cannot coin the metaphor in the first place let alone know whether it is is accurate. Remember -- metaphors can be completely wrong. For instance if a boxer were to fight with huge determination and effort and I said "He fought like a Three-toed Sloth" I would not only cause you to groan at the cliched poverty of my imagination, I would have completely misled you. The metaphor would have been inaccurate.
To take another example: in describing John's tenacity in debate I might say "He worries away at an argument like a terrier". Unless I both perceive John's style of argument directly and I know what a terrier is like then I cannot create the metaphor. You, as listener, only know about terriers (unless you are from a culture that knows nothing of dogs at all - in which case the metaphor is lost on you). You have never seen John but the comparison with a terrier works as it is something with which you are familiar.
Metaphors about God are fine when you simply consider yourself as the recipient of the metaphor. The obscure nature of God can be grasped through the more familiar image that the metaphor offers us. But who creates the metaphor in the first place? How is it possible, and how can the coiner check that the metaphor is accurate?
If the metaphors came to us from an impeccably authoritative source -- from, say, an angel, who had direct access to God then we would not have a problem (except establishing the authority in the first place!). Thus Muslims may have a strong argument here, for their revelation was dictated by Gabriel himself. However, for Liberal Christians, and others who do not believe in Revealed Religion, there is a big problem. If the humans who create the metaphors of Divinity have no special access to God then they cannot know that their metaphors are accurate. To return to our previous example: if I had never seen John argue then I can have no idea of what an accurate metaphor for his style would look like - and if I can't see God directly then I cannot even begin to generate a metaphor to characterise Him.
In the case of God, different types of believer use different metaphors to describe his nature. Some believers will talk of God as an implacable absolutist monarch, so incensed by humanity's disobedience that he is quite happy to see them destroyed by suicide bombers. Others will describe God as a loving father, ready to forgive his creation before they have even repented. How do you adjudicate between these contradictory metaphors? The only way is go back to the original and judge it against the two alternative comparators. However, as we have already established in the case of God, this is impossible because one end of the metaphor, the ineffible Godhead, is beyond human knowledge and experience.
I would therefore suggest that NOTHING can be said of the ineffable precisely because it is beyond experience. We cannot even say it exists. So in Wittgenstein's words, "Whereof we cannot speak, we must remain silent".