I remember God telling Jonah he was going to destroy the Ninevites and then didn't, making Jonah a little peeved.
No he didn't. Read it. Here is God's commission for Jonah:
Jonah 1:1 The word of the Lord came to Jonah son of Amittai: “Go to the great city of Nineveh and preach against it, because its wickedness has come up before me.”
Full stop.
Chapter 3:
Then the word of the Lord came to Jonah a second time: “Go to the great city of Nineveh and proclaim to it the message I give you.”
Jonah obeyed the word of the Lord and went to Nineveh. Now Nineveh was a very important city—a visit required three days. On the first day, Jonah started into the city. He proclaimed: “Forty more days and Nineveh will be overturned.” The Ninevites believed God. They declared a fast, and all of them, from the greatest to the least, put on sackcloth.
When the news reached the king of Nineveh, he rose from his throne, took off his royal robes, covered himself with sackcloth and sat down in the dust. Then he issued a proclamation in Nineveh:
“By the decree of the king and his nobles:
Do not let any man or beast, herd or flock, taste anything; do not let them eat or drink. But let man and beast be covered with sackcloth. Let everyone call urgently on God. Let them give up their evil ways and their violence. Who knows? God may yet relent and with compassion turn from his fierce anger so that we will not perish.”
When God saw what they did and how they turned from their evil ways, he had compassion and did not bring upon them the destructionhe had threatened.
Why send a prophet to a people if their fate is sealed?
The Ninevites repented. They changed their minds, not God.
BTS