:::::You seem to be making  two points here, first that it is relevant ("One presumes that somebody's religious and ethnic background have an influence...") and second that it is not relevant ("I don't see that to be mentioned it has to be relevant to the person's work or fame....").  Given the context of the article it seems that the mention is not just for interest's sake.  If it is relevant, it seems that relevance must be shown, and further, sticking with Wikipedia's verificationist policy (WP:V), it would have to be shown from secondary sources.  Following your other line of reasoning, I am not sure interest is a specific policy.  (Is it? Let me know if it is!)  Either way, what is the source for his religious background?  I don't recall reading it in his books, or hearing it in any interviews I have seen.