The wise one, they stay patient: not too heart-heated, not so hasty to harp, not too weak-armed, nor too wan-headed, nor too fearful nor too fey nor too fee-felching,
my interpretation of this is that those who are wise patiently wait for death. the others who are hot heated, fuelled by passion , or weak mined start conflicts, (like war) later mentioned in the poem. I feel the narrator is advising against that type of violence. This poem was written at a time where there seemed to be tension and conflict with territory.