Ever since the Legion invaded the Exodar, the draenei have been hard at work preparing to return to Argus. At long last they have a vessel that can take us there.
With the way to that dreadful world open, we simply could not ask for a better opportunity to strike. Prophet Velen called for you quite specifically to join the assault force.
You should make your way to Stormwind Harbor right away. Arrangements have been made for a ship there to take you to Azuremyst.