Jonah 3&4 - Consequences when you don't do what the Heavenly Father tells you to do.

Jonah 3:1
Now the word of the LORD came to Jonah the second time, saying,

Jonah 3:2
"Arise, go to Nineveh the great city and proclaim to it the proclamation which I am going to tell you."

Jonah 3:3
So Jonah arose and went to Nineveh according to the word of the LORD. Now Nineveh was an exceedingly great city, a three days' walk.

Nineveh was the capital of Assyria and was situated on the eastern bank of the Tigris River. It was about 280 miles north of Babylon and 400 miles N.E. of Damascus. Some historians say it was much larger than Babylon. The circuit of Nineveh is estimated at 385 furlongs or over 48 miles around. According to the first century BC Greek historian, Diodorus Siculus, it was an oblong parallelogram, extending 150 furlongs in length and 90 furlongs in breadth, and 480 furlongs in circumference. Which computes to about 20 miles long, 12 miles broad, and 60 miles in compass. This agrees with the account given here of its being "an exceeding great city of three days' journey," in circuit. 20 miles a day was the common computation for a pedestrian. It was surrounded by large walls 100 feet high. They are said to have been so broad that three chariots could drive abreast on them. The city was defended by 1,500 towers 200 feet in height.

Jonah 3:4
Then Jonah began to go through the city one day's walk; and he cried out and said, "Yet forty days and Nineveh will be overthrown."

Jonah has just spent three days and three nights in the belly of a whale and probably looked like a walking skeleton. At the very least, his skin would have been completely bleached and rotten. That would give credence to his message and Who it came from. All we are told of Jonah's message is "Yet forty days and Nineveh will be overthrown." This is probably just a summation of his message. The questions of "Why?" and "What must we do to stop this?" are not answered with those few words. It is likely that Jonah was told to tell them what do to to prevent their destruction, which is to turn to the Elohim of Abraham, Isaac, and Jacob, and embrace His ways. Elohim promises that if a nation that He has said will be destroyed turns from their evil ways and turns to Him, He will relent from their destruction. Assyria did, but Judah did not in the days of Jeremiah (Jer 18:7-13). It is likely that Elohim had Jonah go to the most evil Empire in the history of mankind (in that day) to call them to repentance and to show Israel that He would indeed, do the same for them. Elohim would relent from destroying Israel also, that is, if they turn back to Him in repentance.