"A Case of Conscience" by James Blish
I've just finished reading this...has anyone else read it?
I found it deeply thought provoking and I've not seen any book deal with the religous implications of finding sentient alien life (although please let me know if there are).
I suppose I was a little dissappointed by the ending (spoiler follows): It seemed a shame that the Lithian's turned out to be nothing more than a satanic illusion. Why couldn't an alien species exist in such a way that it left no need for the concept of god to be invoked in order to explain it? Why should a perfectly moral society necessarilly need a God to lay down such morals? Of course, it makes sense that one could not possibly arrive at ethical positions by pure reasoning alone, but still...
And of course the book raised interesting questions with regard to our own society. Sure, we don't live in the "shelter" society described by Blish but it is certainly allagorical with our own. Ruiz-Sanchez himselfs wonders whether there has always been a signficant proportion of society completely alienated by the society they live in.