In Iliad 4.78ff., Athene, at the behest of Zeus, comes down to earth to stir up the Trojans to break their oaths to the Achaians so that the war might be resumed and Troy might eventually be sacked (the outcome desired by Hera). Trojans and Greeks are both amazed as they see Athene sweep down to earth ‘between the two hosts.
And thus they would speak to each other, each looking at the man next him:
‘Surely again there will be evil war and terrible
fighting, or else now friendship is being set between both sides
by Zeus, who is appointed lord of the wars of mortals.’
(4.81-4 [Lattimore’s tr.])
At first, this might seem banal and a statement of the extremely obvious (cp. ‘Right now, it is either day or night’; or, ‘In four years, the president will be either a Democrat or a Republican’).
Let us, however, keep in mind the context and the rather peculiar state of limbo in which Greeks and Trojans find themselves at the moment of Athene’s appearance. Her bounding earthward follows directly upon the duel between Paris and Menelaos, which, at least in the view of Menelaos, would lead to the death of one of the combatants:
‘As for that one of us two to whom death and doom are given,
let him die: the rest of you be made friends with each other.’
(3.101-2)
The conflict over Helen was to be resolved by the two most interested parties to the dispute, but Aphrodite short-circuited the duel when she spirited Paris away before Menelaos could finish him off. Agamemnon, to be sure, declared victory for his brother (cf. 3.456-60), who had clearly had the upper hand when the fight was prematurely ended, but the anticipated climax of the single combat is never reached and leaves a sense of the lack of resolution.
Thus, when Athene appears before the Trojans and Achaians, she comes as a divine sign, to be sure. In their state of limbo, they know that something big is about to happen—that the pendulum will swing suddenly to one extreme (hostility) or the other (peace); they just don’t know which one.