"Who knows? God may yet relent and with compassion turn from his fierce anger so that we will not perish." Jonah 3: 9 (NIV)
The king of Nineveh suggests that the people of the great city may not be beyond saving... he calls for confession and for them to repent from their sinful ways. Maybe Nineveh won't "be overturned" (v. 4b) as the prophet Jonah had declared to the people of the city.
The thought of a merciful God is not exactly what most people picture when they think of the 'God of the Old Testament.' Usually, people think of a wrathful, warrior God in the Old Testament stories... so the king's hopes could easily be called overly optimistic. But then again, "Who knows?"
Trying to walk the path that Jesus walked can be an incredibly frustrating task, and frustrations can easily turn to guilt or hopelessness. We can start beating ourselves up over stumbles and struggles, and at these times it's easy to think that we are unforgivable. However, we must learn from the king: recognize your faults, repent, and ask for God's grace and forgiveness... for we know that we worship a God who freely gives grace to all that ask. We must stop limiting God by believing we know the limits of God's grace.
Trust in God's steadfast love, and let God be your provider.