who cannot tell their right hand from their left: God sent his message through his prophetic word in a wicked city. Not everyone who encounters God's light responds positively (see John 3:19–21), but God wants to save those who genuinely repent and have faith.
The book ends suddenly, prompting the reader to consider God's final question to Jonah. God prefers to save rather than destroy. Those who have received his mercy should be happy for that same mercy to be shown to others, even their enemies.