How is the theme of religion and existentialism portrayed in The Sun Also Rises?
The biblical quote that precedes the novel can be taken in two ways that relate to the plot of the novel:
1) there is a hopefulness in the idea that no matter what happens today, the sun will rise again tomorrow...
2) certain things are inevitable. Brett will tease then leave Jake. This is as inevitable as the sunrise.
This particular novel does not strike me as being particularly theological, not as much as For Whom the Bell Tolls and The Old Man and the Sea. What we have in The Sun Also Rises is a group of people striving to create something stable from which they can move on into the future.
Though Jake would like to minimize his vulnerabilities and his perspective on this is somewhat distanced and therefore seems philosophical, I don't know how much intellectual weight we should hang on his character.