The word of the LORD came to Jonah a second time:
“Set out for the great city of Nineveh,
and announce to it the message that I will tell you.”
So Jonah made ready and went to Nineveh,
according to the LORD’s bidding.
Now Nineveh was an enormously large city;
it took three days to go through it.
Jonah began his journey through the city,
and had gone but a single day’s walk announcing,
“Forty days more and Nineveh shall be destroyed,”
when the people of Nineveh believed God;
they proclaimed a fast
and all of them, great and small, put on sackcloth.

When the news reached the king of Nineveh,
he rose from his throne, laid aside his robe,
covered himself with sackcloth, and sat in the ashes.
Then he had this proclaimed throughout Nineveh,
by decree of the king and his nobles:
“Neither man nor beast, neither cattle nor sheep,
shall taste anything;
they shall not eat, nor shall they drink water.
Man and beast shall be covered with sackcloth and call loudly to God;
 every man shall turn from his evil way
and from the violence he has in hand.
Who knows, God may relent and forgive, and withhold his blazing wrath,
so that we shall not perish.”
When God saw by their actions how they turned from their evil way,
he repented of the evil that he had threatened to do to them;
he did not carry it out.

Many times throughout the bible, God uses people to confer a message, just as he did Jonah. “Forty days more and Nineveh shall be destroyed,” he announced, as the Lord bid him. The people of Nineveh believed the words he spoke and feared the Lord – thus they fasted, wearing sackcloths, even the king. All were decreed to fast – all this in hopes that God would forgive them. Indeed, He did repent of the evil he had threated to do and did not carry it out.                                                                                                             

I think the overall lesson from the story of Jonah is God’s mercy – the people made themselves small before God and plead forgiveness, he was willing to give it.  Still in ou lives, no matter what we have done to mess up, turn against him, etc.. He is still willing to offer forgiveness.