The fear of God means that you can listen to him, obey him, and fear his power. Being able to do this means that you will live a good life and know the truth that you can know as a believer live the righteous life that God wants you to live. In other words, if you want to know how to live well, you must respect and obey the Lord first. People who don't understand and are fools refuse to listen to wise teaching because God is telling you the right thing, but when you don't listen you block out the truth so that you can live the life that pleases you no matter how many horrible things you do.
Having fear of the Lord means to want to obey and serve him, that is why it's the beginning of knowledge. You would then want to know how to serve God the right way. You want to be taught about him. The fools in the text are those that don't want to serve God and don't want to be corrected for their wicked ways
Both groups are called Slavs. In the years before World War I, Serbia wanted all Slavic peoples to form one empire, free from rule by the Turks or Austria-Hungary. The Serbs' wish to unite all the Slavs in one empire is an example of. imperialism.
