First, the speaker describes the wise men who "at their end know dark is right." They are wise and so they recognize that death is normal and natural, but "Because their words had forked no lightning they" refuse to die without a fight. This metaphor indicates that perhaps they feel that they have not had enough of an impact on the world the way lightning has an impact.
Next, the speaker describes the good men, who cry "how bright / Their frail deeds might have danced in a green bay." This metaphor seems to suggest that these men feel they could have done more good in their youth (signified by the green bay); they feel their deeds were frail in comparison to what they could have been.
Third, the speaker describes the wild men "who caught and sang the sun in flight / And learn, too late, they grieved it on its way." These men are wild because they really tried to live each moment of their lives without regret—signified by the metaphor of the sun in flight—but they, too, fear that they did not...
(The entire section contains 3 answers and 800 words.)