The three themes are that Go exists, that god punishes those who disobey and that he is merciful at the same time. It is a blend of the demands of Gods people and the punishments as well as the rewards. In essence, it is a complete book that narrates what happens if you don’t follow god’s commands and you sin again and again.
It is important to know that you need to be vary of God’s orders and that you need to understand that there is hope for you if you repent on your sins. This is because god is forgiving and he does not like to punish his men.