I have heard a rumour from the LORD, and an ambassador is sent unto the heathen, saying, Gather ye together, and come against her, and rise up to the battle. I have heard a rumor - The Lord has revealed to me what he is about to do to the Edomites.
An ambassador is sent - I believe this means only that God has given permission, and has stirred up the hearts of these nations to go against those whom he has doomed to destruction.