It's important for all of us to at least become acquainted with this [multiverse] theory because, as Jason [Rosenhouse] points out, it has theological implications — not only about whether our planet is the special object of God’s attention, but because multiverses are relevant to the “fine-tuning” argument for God beloved of religious scientists. Theologians often sneer at the multiverse theory as a ploy atheistic physicists to reject what they see as strong evidence for God. That’s why it’s important (beyond simply keeping up with exciting ideas in cosmology) to know why physicists posit multiverses, and to see that the idea is not something scientists concocted to get around the fine-tuning arguments.
I don't disagree with that. Good on yer, Jerry.
Note, however, that this passage offers us a reason to become acquainted with multiverse theory. It appeals, for example, to our desire to understand whether multiverse theory is a contrivance to get around fine-tuning arguments. If I had no such desire, I could simply shrug all this off and say, "Who cares?" But Jerry is correct to assume that many of us, including me, actually do care about these sorts of things. Thus, when you combine this with some information about the theory, we have our motivation for reading up on it. Although this is only implicit in what Jerry says - he doesn't put it quite like that - it's there. And once again, I agree. He's put forward considerations that will motivate lots of us to read up on multiverse theory if we haven't already, or to read up on it some more.
But what does he have in mind when he offers us reasons for considering whether to read up on multiverse theory? He seems to think that we are capable of thinking about these considerations and coming to a decision to read up on the theory. If we're not really capable of doing that, why suggest that we do it? The point is that even Jerry, who denies the existence of free will, at least thinks that people are capable of deliberating (e.g., I think about the reasons he's offered me for reading up on multiverse theory), coming to decisions (I may decide to go and do the reading up), acting on them (I may actually do the reading up), and producing results (as a result of my reading I may become more knowledgeable and, among other things, better able to debate with theologians).
It's being assumed that we really do deliberate about our actions, make decisions based on our beliefs and desires, and so on. If I didn't think that, I wouldn't offer you facts and ideas to deliberate about. Neither would Jerry if he didn't think something along those lines (but see below!). If I thought all this was an illusion, I'd have no reason to offer you facts and ideas to think about for the purposes of making decisions.
I suppose the comeback might be that I'd do it anyway, since I'd have no choice in the matter! My actions in offering you reasons for considering things might just be "what happens". But really...
None of which settles the meaning of the term "free will", which is all-important to debating whether such a thing exists. But it does at least highlight the difficulty in adopting an error theory in respect of all our everyday discourse about deliberating, thinking things over, making decisions, choosing from options, picking, selecting, and so on. If we believe this kind of talk is analogous to talk about, say, witches - it doesn't refer to anything real - we'd better think through the consequences (though I suppose that would be impossible if we were right!).
If we're going to say that this sort of talk is okay, but that, nonetheless, we don't have free will, we'd better define what message is actually communicated when we tell someone, "You don't have free will."
As I said a few posts back, I'm not in love with the term "free will", which sounds rather grandiose and may not convey anything terribly clear when used outside philosophical discussions where it's defined. But telling someone she doesn't have free will is probably worse - more misleading - than telling someone she does. What she does have, unless her circumstances are very bleak indeed, is considerable ability to make choices that are based on her own values, and which then lead to actions that make a difference to the world.