On the cross we hear Jesus proclaim, with His final breath, "It is finished!" (Literally "It is paid in full.") When the final bowl of God's pent up wrath is poured out into the air (representing Satan's rule in this world) God proclaims loudly from His temple in heaven, "It is done!"
After the fall in the Garden, sin came into the world. In Genesis 3 we the world cursed by God, and the world is writhing under that curse even today. In Revelation 15 & 16, God completes the judgement of sin so the world can be redeemed. In Genesis 3 we meet Satan and sin and in Revelation 15 & 16 we see Satan's kingdom and rule over this world judged and destroyed by God's command.
Revelation 15 is the introduction to chapter 16. (Remember the chapter and verse breaks in the bible are inserted by man for convenience and have NO other significance.) So here is the story of the 7 final judgements of the 21 in the Tribulation. This is the end of the cursed world we live in. Halleluiah!!
So, here are the three lessons that cover chapters 15 & 16 in pretty fair detail. As always, feel free to comment or ask questions on this page.