How is Jake’s and Bill's fishing trip in Chapter 12 of The Sun Also Rises similar to a religious experience?

Jake's and Bill's fishing trip serves as a true respite that is deliberately sandwiched between their daily "lost" lifestyle in Paris and the brutality and debauchery to come at the bullfights in Pamploma. The fishing trip is a peaceful vacation--a meditative lull before continuing on to the bullfights and then back to Paris. Jake knows that San Fermin will be packed with people, so the rural stopover to enjoy his other great love proves to be a much-needed stay. He rids himself of both Brett and Cohn for a while, eliminating two of the people who prove problematic to his daily life. There is no sexual tension or irritating interruptions. Hemingway's pastoral setting and Biblical references--to churches, communion, prayer--along with the unlimited wine (provided with the room) do create a sort of religious experience for the two men. The extravagant lifestyle of Paris is replaced by the simplicity of the quiet country life, and the two men undergo a rebirth as they commune with nature. 

How is Bill and Jake's fishing trip in The Sun Also Rises similar to a religious experience?

The fishing trip is a calm and relaxing experience for Jake and Bill and while they are out in nature together, God's creation soothes their souls, so in this way, it is like a religious experience. Their aimless existence has, for the time being, been left behind. They drink wine together only this time, it relaxes them and they are able to have some meaningful talk AND fall into a peaceful sleep; they say that the wine is strong and that they are "cock-eyed" but they don't seem to get stinking drunk like they normally do when they drink.

Bill says he saw in the paper that his friend Bryan was dead, so when he makes the comment about life not being long on earth, it is reference to this death. Then he makes a comment that mocks a priest's comment right before communion: "Let us rejoice and believe and give thanks." They are eating chicken, eggs and drinking wine - so it is symbolic of a communion service - eating the bread and drinking the wine. They jokingly call each other "brother", again mocking religious people who do this. They are still very cynical about religion, even though they are out in nature and seem to be temporarily happy because of the freeing experience the trout fishing has on them.

Their "mock" religious ceremony, however, relates to the theme of the novel because their lost lives are a mockery of how man is supposed to live while on earth - with joy, not emptiness.