The book of Obadiah records the messages of the prophet Obadiah. As with most prophets, Obadiah’s message focuses on current events — in this case for the people of Edom.
The book of Obadiah is the shortest book in the Old Testament, and nothing is known about Obadiah except that he lived during the fall of Jerusalem. His message was focused on the people of Edom (the descendants of Esau), and was critical of them for their failure to come to the aid of Judah. This message carries with it a sense of justice and does not include any forgiveness toward Edom.
Obadiah is sometimes called a minor prophet. This doesn’t mean he wasn’t important, but merely that the book named after him is shorter. (Compare this to the major prophets, whose books are much longer.)