1. Revelation 18:21 (ESV)
  2. Exposition

Of what significance is the reference to “a mighty angel”?

Revelation 18:21 (ESV)

21 Then a mighty angel took up a stone like a great millstone and threw it into the sea, saying, “So will Babylon the great city be thrown down with violence, and will be found no more;

Angels are God’s servants (Psalm 103:20; Hebrews 1:14). They do not act on their own initiative but obey his will. So behind the action of this angel is the command of God, that is, the exalted and enthroned Jesus Christ.

This angel is mighty. The point of the adjective mighty is not to contrast this angel with weaker angels (who are potentially not up to the task) but to stress the magnitude of what is to happen to Babylon.  More specifically, Babylon (any civilization, state, or city that strives to restore some sort of paradise without God) is great (Revelation 17:5; Revelation 18:2), and in her greatness has wielded enormous influence over kings, merchants, and populations.  To throw her requires a mighty angel.