Yonah did not want to deliver his prophecy to Ninveh because if Ninveh would do tshuvah it would make Klal Yisrael look bad for their lack of repentance. We all know the story of Yonah's attempt to flee, the storm that follows his boat, his being swallowed by a fish, and his eventual delivery of the message. Why, asks R' Chaim Shmulevitz (Sichos Mussar, Shoftim 1971), did Hashem "need" Yonah? Why try to force him off the boat, why miraculously keep him alive in a fish (actually there were two different fishes that swallowed him), why keep after him alone to go to Ninveh? Surely Hashem could find another prophet willing to deliver his message if Yonah refused!
R' Chaim Shmulevitz answers that it was precisely because Yonah fled that no substitute could fill his place. The sensitivity shown by Yonah in trying to avoid any action that might cast the Jewish people in a bad light is what endeared Yonah to Hashem. Who could be more deserving of being Hashem's prophet than someone who evinces such caring?