The poet asks who will follow King Fergus' example and leave the cares of the world to know the wisdom of nature. He exhorts young men and women alike to leave off brooding over "love's bitter mystery" and to turn instead to the mysterious order of nature, over which Fergus rules.
This short poem is full of mystery and complexity. It was James Joyce's favorite poem, and figures in his famous novel Ulysses, where Stephen Daedalus sings it to his dying mother.
On one level, the poem represents Yeats' exhortation to the young men and women of his day to give over their political and emotional struggles in exchange for a struggle with the lasting mysteries of nature. He suggests that Fergus was both brave and wise to give up his political ambition in exchange for the wisdom of the Druids, as depicted in the poem "Fergus and the Druid." Of course, from that poem we know that Fergus' sacrifice was complicated. He did not find a life of frolic and happiness with the Druids. But he did find knowledge, wisdom and perspective - perhaps, indeed, too much.
On a second level, the poem captures Yeats' frustration at his own failed love affair. He seems desperate to turn from the contemplation of love's mysteries that have preoccupied him for so many of the poems in The Rose, convinced that this meditation has only increased his sorrow without providing any means of improving his situation. The exhortation, on this level, is directed inward, to his own heart. He challenges himself to take Fergus' direction and leave love behind him.
Moreover, the fact that Yeats draws upon the imagery of Fergus to make his point suggests his inclination to reference the mythic and legendary heritage of his country rather than the present political struggles that engaged Ireland. In this light, the question, "Who goes with Fergus?" seems to ask Ireland to join him in contemplating the mythic past rather than the sticky present. A return to Fergus entails a move away from the reference points of contemporary politics, toward the mythology of the Irish people.
Finally, the poem suggests the journey toward death. A return to nature, as also seen in the previous poem, "The Countess Cathleen in Paradise," expresses a movement away from worldly cares and possessions analogous to death. Yeats summons the courage that one requires to look beyond the mysteries one knows and suffers under - those of love, of politics - to deeper and weirder mysteries - the wood, the sea, the wandering stars.
In all, the poem has a beauty, especially when spoken aloud, that evades simple readings and analyses. It captures the political, social, emotional and national ambiguity at the heart of Yeats' collection, as well as his reverence for the imagination.