3:1-2 - Now the word of the Lord came to Jonah the second time, saying, “Arise, go to Nineveh the great city and proclaim to it the proclamation which I am going to tell you.”
These verses start the second half of the book. An interesting view of Jonah appears due to the introduction to chapter three: the book is divided in two with each half starting with Jonah's commission. The structure is remarkably similar between the two halves.
1. Jonah's commission
2. Jonah's response (flee/obey)
3. The pagan's response to God (salvation for the crew and Nineveh)
4. Jonah's response to God after the fact (relentance in chapter 2, anger in chapter 4)
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.
Opposed to 1:3, Jonah obeys this time. Nineveh is described as a "great" city in 1:1, 3:2, 3:3, and 4:11. Here we find out that it is massive - a three days walk just to walk around it - upwards of 60 miles in circumference.
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.”
At first read, it appears that Jonah is doing the bare minimum with his preaching, however, the eight word message may have been all God gave. What is an indicator of Jonah's continued reluctance is that while the city is a three days walk, Jonah spends only one day preaching the message.
God's will is realized as Jonah finally obeys and brings God's message to the city of Nineveh. God once again initiates the events of the second half of the book with the same commission as the first half. God's will has not changed.
Jonah's response, of course, does change. Whether begrudgingly or willingly, Jonah does the will of the Lord. The original audience might have reluctantly admitted that Jonah probably should do as the Lord commanded, but they would have still disagreed with it.