Old Major teaches principles of working for the common good, pure equality, and refusal to bow to a master. His ideals are based in themes of revolution against unfair working conditions and human dictatorship.
"Only get rid of Man, and the produce of our labour would be our own. Almost overnight we could become rich and free. What then must we do? Why, work night and day, body and soul, for the overthrow of the human race!"
(Orwell, Animal Farm, george-orwell.org)
When he dies and the animals revolt, they distill his teachings into a set of seven Commandments, with the central tenant that "All animals are equal." As the novel progresses, the pigs use their knowledge to change the laws, giving themselves superior comforts while the other animals work even harder. Old Major's philosophy of equality soon evolves to give the pigs a higher class position than the other animals, with just a single commandment, "All animals are equal, but some animals are more equal than others," showing how the pigs use class warfare and groupthink to control the animals far more than humans ever did.