The book of Jonah opens up with the following command given to the prophet by God: "Go at once to Nineveh, that great city, and cry out against it; for their wickedness has come up before me" (1.2). Jonah, of course, heads in the exact opposite direction, fleeing his divine calling and the presence of God (v. 3).
Now, ignorant of the ending of the book, what reasoning might we impute to Jonah in this situation? Why would he flee? To me it seems plausible that his leaving would have been motivated by a fear of the reception of the message: the people of Nineveh are violent, evil oppressors, and if he foretold doom against them, it might prove to be the last message he ever offers. It wouldn't have been the first time a prophet of Yhwh loses his life because of the message, after all.
Interestingly, however, by the time we reach the end of the story and God spares Nineveh upon repentance, Jonah tells us what his reasoning was: "O LORD! Is this not what I said while I was still in my own country? That is why I fled to Tarshish at the beginning; for I knew that you are a gracious God and merciful, slow to anger, and abounding in steadfast love, and ready to relent from punishing" (4.2). Jonah tells us his motivation was the exact opposite of what we expected: he fled because he knew God would be disposed to forgive the people!
I greatly appreciate the stark contrast here between the world with which the author of Jonah presents us, and the world we may sometimes take ourselves to live in: for the author, God is ready to forgive even the most despicable people, so much so that it may inspire anger in us and in their victims; for us, God's forgiveness is something we dare not trust in, we may hardly be able to believe for ourselves, and certainly we are not so disposed to be quick to forgive, either.
This is something critically important for us if we are to be forgiving people: we have to come to see God, too, as eager to forgive, to restore, to reconcile. So long as we see God's forgiveness as something to be earned with great difficulty, and even then only offered to a certain few people whose sins may not be so grave, we will never be ourselves forgiving in the way we ought to. We will never live up to the example of Stephen, for instance. Jonah invites us to see God as ready to forgive, ready to relent, for the purpose of making us so, as well.