The book of Jonah is unique among the prophetic books. Other books contain the words of the prophet—his warnings, promises, and judgments. But the book of Jonah is about Jonah himself, not just his message.
God told Jonah to go to Nineveh, the capital of Assyria, Israel's bitter enemy. But Jonah didn't want to go. After all, why should the Assyrians accept a message of doom? The Assyrians didn't even believe in the same God. So Jonah disobeyed God and tried to run away.
The rest of Jonah’s story is familiar, even to those who don't know much about the Bible.
After that, Jonah obeyed God and went to Nineveh, where the people repented and turned to the Lord.
The message of Jonah is encouraging. God's love and mercy are available to all nations. And He would rather forgive than punish.