What purpose does religion serve on Napoleon's Animal Farm?
Animal Farm is an allegory about Russia over a span of years in the twentieth century. Like most allegories, the characters and places in the novel are representative of people andplaces outside of the novel (or novella, in this case). Here, Napoleon represents Joseph Stalin, of course, and Snowball is the exiled Leon Trotsky. Moses the raven is a picture of the Church. We know that because he is the one who encourages the animals with the promise of Sugarcandy Mountain.
In this magical place, no animals had to work. Food was plentiful, especially the delectable bits the animals so enjoyed. This promised land, of course, is heaven. Your question is what purpose does religion serve on Animal Farm, and the answer is simple. When the animals were discouraged and tired of working, Moses would swoop in to buck them up, so to speak, with the promise of a wonderful future. This is one more form of propaganda used by Napoleon to keep the animals working and not rebelling. (When he was there, Moses was treated quite well by Napoleon and the pigs.)
The animals grew to resent Moses, for he did no work and told tales, consuming without producing, much like the pigs. He even got bread crusts soaked in alcohol when he returned to the farm for good. There was ultimately no difference between him and the pigs.