This passage is talking about when God flooded the world for forty days and is now creating a new earth. No one will remember what the earth was like and will rejoice in the new world God has created for his people. God says “I will rejoice in Jerusalem and exult in my people”. This is referring to when God sends his only son Jesus Christ to Jerusalem to save us from sin. The world shall not be a place of sorrow or sadness, but a place of joy and happiness.