The central argument of Old Major's speech is a call for rebellion and freedom from human oppression. He encourages the animals to unite against their human oppressors, emphasizing the idea that humans are the source of their misery. rephrase like 8th grader

Old Major's speech is basically saying that the animals should stand up against the mean humans and be free. He wants them to join together and fight against the humans because they are the ones causing all their problems.