Eagleton’s touching foray into theology shows, if proof were needed, that he is no philosopher: God does not have to exist, he informs us, to be the 'condition of possibility' for anything else to exist. There follow several paragraphs in the same fanciful and increasingly emetic vein, which indirectly explain why he once thought Derrida should have been awarded an honorary degree at Cambridge.
Of course, this might have been a more devastating witticism were Grayling actually reading the passage very carefully. This is the section of Eagleton's review that Grayling is mocking:
For Judeo-Christianity, God is not a person in the sense that Al Gore arguably is. Nor is he a principle, an entity, or 'existent': in one sense of that word it would be perfectly coherent for religious types to claim that God does not in fact exist. He is, rather, the condition of possibility of any entity whatsoever, including ourselves. He is the answer to why there is something rather than nothing. God and the universe do not add up to two, any more than my envy and my left foot constitute a pair of objects.
(1) Eagleton does not present it as his own view, but links the claims to a context, one that is explicitly mentioned in the first few words. In fact, in the very next paragraph he reiterates this.
(2) Eagleton, unlike Grayling (who is tripped up repeatedly by this, not only here but also elsewhere), recognizes that people use words in different ways, and that you have to be sensitive to different usages of terms. Note, for instance, the 'in one sense of that word'. And Eagleton is factually quite right: there are theologians who, while allowing that God exists, prefer to use the term 'existent' in a more restricted sense to mean that which has being from another, reserving 'being' or some other term for God (who does not have being from another). This is a purely verbal matter of convenience.
Grayling is right, though, that much of Eagleton's review indirectly explains why he objected to the attempts to block the honorary degree for Derrida: his protest then was that the people who were attempting to do so were lying about what they were criticizing -- that you could tell they had not read Derrida because they repeatedly said false things about what he said, and didn't care whether they were false as long as it stopped Derrida from being awarded the degree. And it must be admitted that his protest against Dawkins is very much the same: that Dawkins is spreading false claims about religionists in a way that shows that he doesn't care whether he has any rational basis for his claims or not, as long as it leads to the necessary conclusion.
Eagleton doesn't mention this one in particular, but one case that he might, that might clarify why Eagleton's point can't be airily dismissed in the way so many Dawkinsians seem to want to do. Dawkins, in order to dismiss the idea that the civil rights movement was religious in inspiration, simply says, without serious argument, that religion was completely incidental to Martin Luther King Jr.'s fight for civil rights, that although he happened to be a Christian, he got all his ideas from Gandhi, who was not. As some have noted, if you really want to play that game, you can say that Gandhi got his ideas from Tolstoy and Jesus. But what is really disturbing about Dawkins's claim is not that he made it, but the sheer disregard for evidence and reasoning it seems to evince. Historians studying Martin Luther King and the civil rights movement, you apparently needn't bother with the Social Gospel movement, or Boston Personalism, or the religious themes in King's speeches and sermons; acording to Dawkins, they are all incidental. And he took his ideas from Gandhi, anyway! What sort of response is that to the idea that King's fight for civil rights was religiously inspired? Perhaps it was just a mistake, or a confusion, or he just got carried away with hyperbole and only meant to say that people exaggerate the religious inspiration of King's ideas, or he just didn't realize that we readers lack the telepathy to be able to see immediately the great argument he has for an apparently insupportable claim; but it looks a lot like the sort of response you make when you don't care what the evidence is or where reason actually leads. Again, on its own perhaps it's just a slip, or just a perhaps-overly-concise or misleading claim that Dawkins could really develop with greater seriousness than he does. What would really be damning is if he did this all the time. And that's what Eagleton is claiming -- that he does do this sort of thing over and over again.
And if he is, Eagleton is exactly right: it's a sign of someone who either does not know the actual evidence and arguments, or (more culpably) of someone who doesn't care what they are. In either case, he's an unfortunate distraction from the real issues. What has amazed me is that the most general response to Eagleton has not been to argue that Dawkins is in fact informed about the subject he is criticizing, so that his criticisms are genuinely devastating; rather, it has been to agree that Dawkins is badly informed about the subject, and then to come up with an excuse for why that's entirely OK, because the subject is not worth the time to make an effort to be informed about it. (One wonders, then, what would be the point of writing a book about it.) Grayling for instance, in the paragraph before the one above, claims that "when one rejects the premises of a set of views, it is a waste of one’s time to address what is built on those premises," somehow missing the fact that Eagleton's point is that Dawkins has misunderstood the premises, and the conclusions claimed to be derived from them, in the first place.