In the Hebrew, this sentence is only 5 words long.  It doesn’t even mention God, nor did it call the people of Nineveh to repentance.  So why did the Ninevites believe what Jonah warned them of?  Jesus tells us in Luke 11:29-32 that the Ninevites had heard of Jonah’s miraculous deliverance from the belly of that fish and that they will, “stand up at the judgement with this generation and condemn it; for they repented at the preaching of Jonah, and now one greater than Jonah is here.”  The people of Nineveh heard and believed God…may this present generation do the same.