Harry Harrison's "The Streets of Ashkalon" aka "An Alien Agony" aka "The Streets of Askelon" (short story, religion, free): Religion creates sinners!
Story summary.John Garth is a human trader who has been for the past year living among intelligent alien aborigines, amphibians called Weskers - the only human on this "Wesker's World". Then, one fine day, a Christian missionary arrives - one Father Mark of the Missionary Society of Brothers.
So we see the willing students that these aliens are torn between rational John & fanatic Mark. Since the aliens are intelligent & have learnt scientific method from John, they decide to give Mark's teachings an empirical test: he gets the Jesus Christ treatment on a cross! And now aliens are awaiting his resurrection...
- "In Trader Garth's books there is the universe which we have not seen, & it goes on without God, for he is mentioned nowhere... In Father Mark's books He is everywhere & nothing can go without Him. One of these must be right & the other must be wrong."
- "Nothing created God, since He is the Creator. He always was ..."
"If He always was in existence - why cannot the universe have always been in existence? Without having had a Creator?"
- "Have faith, that is all you need. Just believe."
"How can we believe without proof?"
- Wikipedia has this to say on the "The Streets of Ashkalon" title of this story: 'Its name is a reference to a passage from the Biblical 2 Samuel 1:20, which says "...proclaim it not in the streets of Ashkelon..." In the original context it was a part of a story in which Hebrews were instructed to try to keep the defeat of a couple of their war heroes from their enemies' knowledge'.
Fact sheet.First published: New Worlds Science Fiction, September 1962.
Download full text from Shortcovers.
Credits: Shortcovers download link is via Free SF Reader; I haven't read this online version, however. Some of the bibliographic information here comes from ISFDB.
Related: Stories of Harry Harrison.