The main subject of this section is God's compassion, which is willingly bestowed upon the deserving. Whereas the previous section contained immediately present and observable threats to the very lives of the people involved, in this section it is merely Jonah's admonition that is required to turn the people of Nineveh back on to the path of righteousness. Upon hearing his words, even the king reduces himself to fasting and sackcloth, and requires the same turning to God of all the citizens and even the livestock that live within the city. This total devotion to God from a mere reminder of his due is enough to restore God's compassion and dissuade him from his punishments.
The third section, comprised of the fourth and final chapter...
Jonah is first angered that the city of Nineveh will not be punished as God had threatened, and he is then angered by the loss of a vine that had grown to provide him shade. God points out that he had nothing to do with the vine's growth -- which only when Jonah had sat down -- or its death, which occurred a day later, therefore he had nor right to anger over the matter. This is a clear parallel to Jonah's feelings regarding the city, which are completely unwarranted because Jonah did not invest himself in the city's success or obedience to God. Questioning God is not Jonah's major sin; it is his anger.
