The Book of Jonah and The Days of Awe, Professor Jeffrey H. Tigay
The oldest Jewish interpretation of the book holds that Jonah fled because he wished to protect his credibility. Since the Ninevites were sure to be forgiven, Jonah, who was to predict their doom, would look like a false prophet.10 A variation on this view holds that it was God's credibility that Jonah sought to protect. God's willingness to forgive and forget would destroy the fear of God; His word would become a mockery and men's trust in Him would be shaken if His threats were so easily evaded.11 The book does raise this problem. The divine threat is phrased in absolute terms; even a date is set. Yet after forty days Nineveh remains standing...
...This is a view of prophecy that Jonah apparently did not share. He was a member of the old school. The Book of Deuteronomy had defined a simple test for the truth of a prophet:
If the prophet speaks in the name of the Lord and the oracle does not come true, that oracle was not spoken by the Lord; the prophet has uttered it presumptuously.... (Deuteronomy 18:22)
Under this conception the job of prophecy seems simple: Speak what God tells you and you will always be proved right. History is intelligible, God's word always comes to pass, and the prophet is a celebrity. But how tragic is the new conception! Speak what God tells you, but speak it so effectively that the people will be moved to change their ways and thus obviate your dire prediction (cf. Jer. 26:18-19). If your reputation suffers in the process-that's a small price to pay for what you will have accomplished!