The Lord gave this message to Jonah son of Amittai: “Get up and go to the great city of Nineveh. Announce my judgment against it because I have seen how wicked its people are.”Let's put the account of Jonah in a little context. From the historical view we again must back up in time a little. Jonah lived about 200 years before the Babylonian exile and just before Isaiah lived. The Assyrian empire is at the peak of it's power in the Middle East and Israel's great enemy. Nineveh is the capital of the Assyrian Empire. Geographically, Nineveh was "on the eastern bank of the Tigris near the modern-day major city of Mosul, Iraq which lies across the river."
...But Jonah got up and went in the opposite direction to get away from the Lord. He went down to the port of Joppa, where he found a ship leaving for Tarshish. He bought a ticket and went on board, hoping to escape from the Lord by sailing to Tarshish.
...“Throw me into the sea,” Jonah said, “and it will become calm again. I know that this terrible storm is all my fault.”
...This time Jonah obeyed the Lord’s command and went to Nineveh, a city so large that it took three days to see it all. On the day Jonah entered the city, he shouted to the crowds: “Forty days from now Nineveh will be destroyed!” The people of Nineveh believed God’s message, and from the greatest to the least, they declared a fast and put on burlap to show their sorrow.
...When God saw what they had done and how they had put a stop to their evil ways, he changed his mind and did not carry out the destruction he had threatened. This change of plans greatly upset Jonah, and he became very angry. So he complained to the Lord about it: “Didn’t I say before I left home that you would do this, Lord? That is why I ran away to Tarshish! I knew that you are a merciful and compassionate God, slow to get angry and filled with unfailing love. You are eager to turn back from destroying people. Just kill me now, Lord! I’d rather be dead than alive if what I predicted will not happen.” (New Living Translation)
So God tells Jonah to go to Nineveh the capital city of Israel's enemy. He probably hated these people and wanted nothing to do with them. God wanted him to warn the people of Nineveh that they would be destroyed because of the evil that was rampant among them. Jonah had no problem with these people being destroyed, but he was concerned that God's compassion and love would save them not destroy them. That's why he didn't want to warn them. He didn't want to give them a chance to be saved.
God is Holy. Once again we see a Holy God who does not want to destroy people for their sin, but God must destroy evil. His holiness and justice demands it. God is Love. Because of his love his desire is that people will turn away from sin and towards him. Later from this point in history God proves his love in an a remarkable way.