"For Him I Sing" is a poem with vague symbolism in which the speaker sings "for" an unidentified "him." The speaker compares the process of raising the present from the past to growing a tree from its roots. He describes "his" movement through space and time, and ends by saying that he has fused the immortal laws to make "him" a law unto himself: in other words, "he" is the ultimate authority and the ultimate figure.
Although the pronoun "him" never has any clearly defined antecedent in this poem, Whitman means "him" to represent his ideal self, which only exists within his imagination. Whitman clearly admires this version of "him" and believes that he possesses the ability to grow the present out of the past. This ideal man is worthy of being "the law unto himself," which is possible if all immortal laws fuse together. In Whitman's eyes, only a poet is worthy of this power and distinction—so it is clear that this ideal "him" is a poet.
The poem is made up of a single stanza containing five lines, and just like the majority of Whitman's other poems, it is written in free verse without an established rhyme scheme or meter. The brevity of this poem makes it seem like a small or fleeting thought. It is a snippet from Whitman's mind, a brief image of an unattainable ideal for the reader to glimpse. When it is over, both Whitman and the reader return to the flawed reality.
A subtle religious undertone is present in the poem, as there is a possible parallel between the mysterious "him" and Christ. By presenting "him" as a Christlike figure, the "law unto himself," Whitman expresses his belief that poetry is sacred, and that poets have the power to perform godlike actions with their words.