Andrew M. King has a helpful article on the book of Amos, where he walks through the key themes of the book of Amos. His summary:
Though only in seed form, the book of Amos signals God’s redemptive purpose seen in the whole of Scripture. From beginning to end, the triune God of creation and covenant is shown to be faithful in judgment and salvation for the fame of his name.
King does a great job tracing the pieces of these themes throughout Amos’s prophecy. Accordingly, he is focusing more on the contents than on the argument of the book (the opposite of what I attempt to do in my interpretive book overviews). However, his piece is a great example of why it is also important to also understand the contents of the books we study.