Gulliver, in being thrust into situations where the size differential between himself and others is exaggerated, becomes the Other: a person who is an outsider and does not conform to the thoughts and values of society. This theme may not have been Swift's main intention in the Lilliput and Brobdingnag sections of the book, but it's at least a side effect of his other messages. Swift felt himself an outsider in his own life, so it would be strange if he didn't have at least an unconscious sense of himself as Gulliver.
The episode in which Gulliver, as a giant, puts out a fire by urinating on it is especially important. Though the effect is comical, it makes a serious point. Gulliver is only trying to do good, but he's criticized by the Lilliputians for public indecency. The incident is a symbol of the misunderstandings among people because of prescribed codes of behavior. This has been an endlessly repeated problem in human society. So are disputes about trivial matters in religion, politics, and other areas of actual life. The Lilliputian dispute about the proper way of cracking an egg is Swift's metaphor for such arguments among people.
The final journey of Gulliver is usually considered the most far-reaching and troubling part of the book. The scenario in which humans have become degraded animals ruled by intelligent horses has been interpreted innumerable ways. Probably Swift intended it either as a warning of what men can degenerate into, or as a picture of what men in their worst behavior already are. His point may be to pose a question: are people who slaughter each other on a massive scale in war—as occurred in Swift's time and still occurs now—better than the "savage" Yahoos?
One of the biggest social issues that this text considers is whether we should allow social life to be driven by power or morality. Let us remember that Gulliver experiences a variety of states in his travels, and interestingly in Lilliput he experiences the advantages of being massively strong and powerful to the point where is able to single-handedly defeat the Blefuscudian navy. At the same time, however, he is also shown to be tiny miniature human in the world of Brobdingnag where the sheer size of everything else means that even insects prove to be a significant challenge for him.
However, alongside the use of physical force in the worlds that he visits, there are also plenty of references to morality being used as a governing power. For example, the way in which the Houyhnhnms use physical force to repress and keep the Yahoos down is justified by their belief that they are morally superior: they, after all, are far more rational and know how to behave and look after themselves.
We can easily link such approaches to troubling and problematic modern day questions of beliefs in cultural superiority. It is often assumed, for example, that Western society is more liberating and freer than Islamic society, especially for women. This assumption however becomes incredibly problematic when we act on such beliefs by responding with physical force. In the same way, the novel shows that claims of a higher system of morals often are used to mask the power of strength. For example, the Laputans keep control of the lower land of Balnibarbi through their military might because they think they are more rational. In the same way, it was a moral imperative in part that led to the widespread colonisation of many parts of the world. The novel forces us to consider that in our relations with others, claiming to possess a higher system of morals is just as problematic as outright physical might.