The poet bids a sad farewell to his fancy, his imagination: "Farewell dear mate, dear love!" He doesn't know where he will go or whether he will ever encounter his fancy again. For a long time, the poet and his fancy "lived, joy'd, caress'd together," and now comes the moment of their separation. Yet there are no regrets because the poet has become almost one with his fancy. He even hopes to be united with her again. Maybe in leaving him, fancy is really ushering him "to the true songs," and therefore he declares: "Good-bye — and hail! my Fancy."
This is the final poem of Leaves of Grass proper. The central core of the poem is Whitman's identification with his fancy; and what is identified is the poet's body, not his soul. The "I" in this poem is the body, and the farewell is prompted by the body's impending dissolution. The tone of the poem is surely plaintive, but the poet's pessimism is not very deep. Whitman slowly and steadily realizes the true importance of his association with his fancy. The union between body and fancy paves the way for the transformation of the physical world, since fancy has the power to enable the poet to visualize the world of bliss.
Despite the serious nature of the theme, Whitman has maintained an informal, intimate tone and atmosphere in the poem. The diction is colloquial — for instance, "let me look back a moment" and "may-be we'll be better off." Finally, this poem expresses Whitman's belief that fancy will conquer death and be a harbinger of immortality.