In order for a person to realise their need of repentance they need to see their sinful condition. The Bible is a mirror to the sinner to show them their true condition.
A person who reads the Bible in his sinful condition will imagine that God acts like himself in dealing with situations. When people test the patience of God, we imagine can easily be tempted to think He will be angry. The Bible is written in a way that can reflect our natural thinking but this is to show us our sin.
Once we understand the life of Jesus when He came to earth we can truly know what God is like and then we can grasp that before this we imagined God to be like us - one who gets angry and will execute people who are evil.
This presentation is a pivotal chapter in the book. If you grasp this chapter many things will start to come together.