What is the meaning of "Hopeless, there stand the purple jars/ Of night to spill oblivion"

I'm not going to write 150 words lol, but i will you with giving you examples of how they kept the animal population from revolting. napoleon made a list of rules, and told everyone how "important they are even though he was known to break them and then have them changed by the only animal who could read on the farm. none of the animals were intelligent enough to read, so they never knew if they had been changed or not which was an advantage to napoleon. napoleon constantly reminded them that if they revolted they would have to go back to mr. jones' way of things, which in retrospect was "worse" (wasn't really worse though, he was just saying that to intimidate since he didn't wanna lose his power). one of the main reasons they revolted in the first place was food, and of course if they revolt napoleon will not share food with them.