Gulliver's Travels has a stereotyped reputation of being a children's book. People who think this obviously haven't read the book. Swift's novel is about many things, some of them rather obscure, since the book makes numerous hidden references to people and events of the day. In spite of this dense allusiveness of the book, though, it deals with perennial issues that we deal with even today.
One of the things the novel is concerned with is, ultimately, original sin. Swift's depiction of the multifarious ways in which humans are grotesquely distorted from their created purposes is sometimes hard to face, even when couched in ridiculous satire. The novel ultimately reflects humanity back to itself, showing us what we look like without redeeming grace.