This quote is important because it demonstrates how the farm moved from animalism to totalitarianism.
Old Major’s dream has all of the animals being equal and living in harmony with no one being more important than another. As it turns out, the pigs begin taking control almost immediately. The pigs are described as clever as early as chapter 1, when they learn the song first. In chapter 2 it is noted that the pigs “were generally recognised as being the cleverest of the animals.” Because the pigs are the organizers, they are able to start taking over. They begin by taking the milk and apples and go from there.
By the time the animals adopt this ironic slogan, all of the animals except the pigs are equal—they are subservient to the pigs.