This short paragraph first introduces us to a mighty angel (Revelation 18:1–2a), then his message (Revelation 18:2b, Revelation 18:3. The message itself has two parts: Revelation 18:2 paints the picture of the situation, and Revelation 18:3 provides the reason why.
1 After this I saw another angel coming down from heaven, having great authority, and the earth was made bright with his glory.