Babylon is a symbol of the entire world's system for economics, politics and military rule. The wickedness was very great, forsaking the true God, setting up idols, and had drawn all sorts of men and women into immoral lifestyle, spiritual adultery and false worship. By deceitful manner, people get rich, and by their wealth and luxury, this evil system had kept the people's interest. John tells that the Lord has people in Babylon, but He called them to get out from it, and not to partake in their sins, or else they shall receive their plagues too. The kings and political leaders of the world mourned as they saw the collapse of the entire world. The merchants and businessmen wept too because no one buys their merchandise anymore (v11). The riches of the ungodly people will avail nothing, and their love for money shall bring them to their own destructions. They lament not for the anger of God, but for the loss of outward comforts. On the other hand, the heaven rejoices, including the apostles, prophets, and all believers, for God had judged evil men for our sakes. Indeed, God is alive, and He knows all things. God bless.