Why do the pigs allow Moses to preach about Sugarcandy Mountain in Animal Farm?Also, what is the fable or moral of the story?
The fact that the pigs allow Moses to come back on the farm is supposed to show just how far they have gone toward being just like the humans they replaced in the revolution.
The pigs have gotten to be so much like the humans that they need Moses to come back and fulfill the same role he did before. They need him to distract the animals from thinking about how bad their lives are now and to get them to focus on the possibility of a better life after they die.
Moses is doing what Marxists say religion is for -- he is being the "opiate of the masses," helping them to feel better even though their lives on earth are terrible.