The image here is of an envoy or messenger, sent by the Lord, to gather the nations to get ready for battle against Edom. It is not clear who this envoy is, but the message is clear. The Lord will make you (Edom) small among the nations, despised among mankind.
Any sense of status that Edom had among the nations will be destroyed in defeat. The horror you inspired has deceived you and the pride of your heart, you who live in the clefts of the rock, who hold the height of the hill.
Edom believed that the physical defenses of their land gave them a measure of impunity in committing atrocities against other nations, especially the people of Israel. They were blinded by their pride that came from their false sense of security. “Though you make your nest as high as the eagle’s, I will bring you down from there declares the Lord." They have failed to consider the Lord. From him there is no defense. He will bring them down both from their places of physical security, but also from their pride and attitudes of impunity.
The envoy's message to Edom is a devastating one, but the irony is that Edom had sent an envoy to Jerusalem to plot against Babylon (Jeremiah 27:3).
14 I have heard a message from the LORD, and an envoy has been sent among the nations: “Gather yourselves together and come against her, and rise up for battle!