The novel (it's more of a short story, if I recall correctly) by Zelazny you are thinking of might be A Rose For Ecclesiastes. It does deal with an alien race which is dying and how they manipulate an Earthman into 'redeeming' their civilisation, but destroy him emotionally in the process. I think the civilisation was a Martian one. You can try one of his anthologies to find it, such as "Four for Tomorrow" or "The Doors of His Face, the Lamps of His Mouth".
On Fri, 7 Feb 2003, Deb Warner wrote:
> MAN". There is also a story involving a missionary to
> ETs who brings the traditional message of death and
> redemption to ETs, and ends with him being crucified
> by the empirically-minded ETs. Don't remeber the
> author title but suspect that it may well be by Zelazny.
That sounds much like "The Streets of Ashkelon" by Harry Harrison. An
excellent story. It's most recent appearance is in 50 IN 50 from Tor, but
it also appears in BEST OF HARRY HARRISON (1976) and STAINLESS STEEL
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