So for this, you have to read The Prose Edda, which was put together by Snorri for the purposes of teaching people how to do ON poetry and diction. It lists several kennings, poetic terms that you can use in place of a single word (Röskva's brother is Thor, Wolf's father is Loki, Ägir's fire for gold etc.). If you were an ON scald, you'd have had to know them all, and then you'd know that "the eagle will be fed" alludes to the fact that there will be battle and people will die (the eagle will feast on the remains of the corpses). Another term for a warrior is "Destroyers of Eagle's hunger". For example, in Egil's saga it says thus:
The edges swing,
Blades cut men down.
Eirik the King
Earns his renown.
The ravens dinned
At this red fare,
Blood on the wind,
Death in the air;
The Scotsmen's foes
Fed wolves their meat,
Death ends their woes
As eagles eat.
Carrion birds fly thick
To the body stack,
For eyes to pick
And flesh to hack:
The raven's beak
Is crimson-red,
The wolf goes seek
His daily bread.
The sea-wolves lie
And take their ease,
But feast the sly
Wolf overseas.