It begins, “The word of the Lord came to Jonah the son of Amittai…”
Chapter 3 begins, “The word of the Lord came to Jonah a second time…”
Communication number two is more than chronologically second: it is different in nature.
The first communication is peremptory: “Go to Nineveh and proclaim judgment against (al) it!”
The second seems to contain room for manoeuvre: “Go to Nineveh and proclaim to (el) it what I tell you”.
In both texts, Nineveh has sinned, but in the first case there is no way out: judgment has been issued and Nineveh must be punished.
In the second case the prophet can establish rapport with the city and presumably imply that they still have a chance of repentance.
The final result is indeed an act of repentance, as we see from the end of Chapter 3, though Jonah is not too impressed to see God showing mercy to the city.
The commentators are not sure why Jonah was so put out – was it that he was something of a racist and did not want to see a gentile city escape destruction? Was he afraid that Nineveh’s escape would put Israel in a bad light?
Israel had also sinned but were too stiff-necked to repent, whilst Nineveh listened to the call to penitence and turned to God.