Jim Slagle points me this morning to a post of his that links to four papers by David Lewis on religion from Andrew Bailey's Lewis page. (Occasional MavPhil commenter Bailey deserves high praise for making available online papers by van Inwagen and Lewis.) Slagle goes on to make some criticisms of Lewis with which I agree.
Since Lewis "didn't have a religious bone in his body" as I recall his wife Stephanie reporting in an A. P. A. obituary, a serious question arises: if you don't know a subject-matter from the inside, and indeed by sympathetic practice of that subject-matter, how seriously should we take what you have to say about that subject-matter?
For example, how seriously ought one take a philosopher of law who has never practiced law or who doesn't even have a law degree? How seriously ought one take a philosopher of physics who has never done physics? Such a philosopher does not know the subject from the inside by practice. Equally, how seriously should one take a physicist such as the benighted Lawrence Krauss who does not know philosophy from the inside, by practice, yet pontificates about philosophical questions? In the case of Krauss, though not in the case of all such physicists, we should not take him seriously at all.
To be a good philosopher of X one ought to know both philosophy and X from the inside, by practice.
Why should it be any different for the philosophy of religion? I incline to the view that one should not take too seriously what a philosopher says about religion unless he knows religion from the inside by the sincere and sympathetic practice of a particular religion. David Lewis, without a doubt, was one of the best philosophical practitioners of his generation. And yet he understood nothing of religion from the inside.
I am not saying that we should dismiss what Lewis says about religion. I am saying that we should not take it too seriously. He literally doesn't know (by sympathetic practice, from the inside) what he is talking about.
It cuts the other way too. What many if not most religionists says about philosophy is stupid and pointless because it 'betrays' no understanding of philosophy from the inside by sympathetic practice.