I think that one of the most powerful ideas that comes out of Orwell's work is how individuals can be manipulated by those in the position of power. Contrast Boxer and Squealer. The ability to manipulate and the dreadful condition of being manipulated are both a part of this equation.
Squealer represents the basic idea that those in the position of power will do just about anything to maintain it. Squealer's gift of "spin" is something about which Orwell was prophetic. He understood immediately that governments that are able to twist what is being done into a manner that confounds and confuses the body politic are ones that have a greater chance of control and power. Squealer's gift to spin everything to legitimize the Pigs' rule and, in general, Napoleon is something that embodies the idea of modern politics. Orwell understood that the modern condition of political rule resided in the ability to spin and the ability to control through language how individuals think and perceive. This idea is something that has not dissipated, but actually grown and increased over time.
Boxer is loyal to a fault. Boxer believes in the revolution, zealously supports "Comrade Napoleon," and never really questions anything being ordered with a sense of certainty and absolutism. He works tirelessly, extra hourse sometimes in order to accomplish what is asked of him. His blindness in "Napoleon is always right" and "I will work harder" represents the body politic's need to appease those in the position of power. It also represents his own doom. His inability to read and his trust cause him to be taken to the knacker. All he can do is faintly hear Clover's warnings. As he kicks and kicks the inside of the van, it comes to no avail, and slowly, his kicking dies down. He dies some time later. Boxer represents the idea that if citizens do not get "turned on" to politics, politics will "turn on" them.
Orwell uses both characters to enhance his idea of what modern politics resembles. The trust of the people match beautifully and quite horrifyingly with the lack of trust offered by the government. This becomes his central idea, the driving force, behind the work. In assessing the idea of trust in the modern political setting, Orwell is forcing the reader to make some critical assessments in their own relationship with their government, to discern where Squealers exist and how to avoid Boxer's fate.
it's about greed, it mirrors the faults of leadership whose effects are felt by the people represented by the animals as the chief characters of the novel.