Like the Old Testament angel of the LORD (see Genesis 16:7–11; 22:15; Exodus 3:2; Numbers 22:22–34; Judges 2:1–4; 6:11–22), the angel coming down from heaven has God's authority. This is symbolized by the key that controls the bottomless pit and the power to chain God's great enemy (see Revelation 12:7–9) for a thousand years.
See the "The Thousand Years (The Millennium)" Theme Note.