Judge Posner on exclaustration and the Constitution

Over at The Volokh Conspiracy, Eugene Volokh has the story about the Seventh Circuit's recent and fascinating decision  about the alleged defamation involved in calling someone a "fake nun."  Here's a bit from the (I think correct, for reasons I wrote about here) decision:

A secular court may not take sides on issues of religious doctrine. The district judge in this case has ruled that a federal jury shall decide whether Patricia Fuller is a member of a Roman Catholic religious order, though if the jury decides that she is it will be rejecting the contrary ruling of the religious body (the Holy See) authorized by the Church to decide such matters. 

A secular court must be allowed to decide, however, whether a party is correct in arguing that there is an authoritative church ruling on an issue, a ruling that removes the issue from the jurisdiction of that court.... But once the court has satisfied itself that the authorized religious body has resolved the religious issue, the court may not question the resolution....