Graham Harman, on replying to Steven Shaviro here, writes the following,
"As for Whitehead, I’m not sure I know what Steven means when he says the eternal objects are there as a source of novelty rather than a source of connection. The point is, prehension is always mediated by the eternal objects, and the eternal objects are in God. It’s hard to be more of an occasionalist than to say that God is the mediator of all relations and that entities exist only as occasions. It’s textbook occasionalism, in fact." (full text)
Matt of Footnotes2Plato is right; Harman is leaving out much Whitehead to make those claims about Whitehead and occassionalism.
The "eternal objects" are analogous to Peircean "pure possibility" and invoke a scholastic realism of universals. That is, it is the view that universals are not just words that humans use to order their experience, which is nominalism and Peirce's foe, but have being though not existence. (There are exactly three modalities of being for Peirce.) If the eternal objects are not real, have being, then we run into the British Empiricist or Lockean problem of asking what "dogness" is if we have only a general (generated) idea of it formed from a habit of recognizing impressions. Even Kant doesn't sufficiently get us out of this problem.
This is why eternal objects matter. Their necessity is not supposed to be a mystery. The logical implications seem messy and counter-intuitive because so much of the last few hundred years of philosophy has been nominalism, and even so-called "realism" is often crypto-nominalism. I am not saying that the solutions are easy or can be laid bare, but we should be aware of the problem, especially since obeissance to neuro-philosophical models makes it too easy to slide into a facilt nominalism.
Finally, Harman's statement that the eternal objects are "in God" is just playing on an unanalyzed spatial metaphor that some readers will accept without thinking due to its conventionality. The "in-ness" is not totally misguided as God has a special relation to the eternal objects as Matt discusses. I think Levi Bryant is right in the sense that we do not have to call this "God," although the logical necessity of the "God-function" makes the term an apt choice ... except that we live in even more atheistic times than Whitehead. Perhaps we forget that. Matt is right to connect God and participation, and it does not hurt to think about what Plato said about "participation" if one can hold oneself back from accusing Whitehead of being a Platonist.
In conclusion, I am taking Harman's statement to be an off-hand comment masquerading as a thoughtful one. I make plenty of offhand comemnts before--I recently mixed up "generals" and "universals," which makes the Baby Peirce cry.