That the Order isn't dead, that the Empire didn't destroy it. Luke is a symbol ... in the Jedi and still felt that grief knowing they were all gone. From facing her old master, Anakin Skywalker ...

As far removed from the Jedi as Cassian ... by Ahsoka Tano after Order 66 and the fall of the Galactic Republic, originates from a secret communications channel that Anakin Skywalker would use ...