The poem directly addresses the successive themes in Whitman's poems. The speaker begins by claiming that the poem is an ode to "One's-Self" - an individual. He then immediately expands the scope of the poem by applying it to individuals "en-masse," emphasizing the democratic nature of the work. According to this poem, Whitman's ensuing poetry will encompass both the individual and the collective, democratic mass, drawing many parallels between them. The speaker further asserts that he "sings" (or, as a poet, writes) about the body, about both men and women, about life and passion. The poem concludes with the idea of The Modern Man, an ideal of American society that Whitman hopes to attain through his poetry.
"One's-Self I Sing" is the first poem in Inscriptions, which is the first book of Whitman's Leaves of Grass. The poem sets the tone for the rest of the volume because Whitman introduces the themes that he, the poet, will "sing" about. The poem delves into themes of the self, the all-encompassing "I," sexuality, democracy, the human body, and what it means to live in the modern world. Though this poem is short, it alludes to the broad scope of ideas that Whitman will explore in the rest of the poems in Inscriptions and Leaves of Grass.
Whitman speaks to a general idea of self, a commonality between his personal identity—the Walt Whitman he so often casts as the protagonist in his poems—and the Democratic self, which is the collective identity that everyone shares. Whitman explains that the self is a shared experience between the poet and the reader. As members of a democratic society, all selves are intertwined—but conversely, each of these intertwined "selves" still retains his or her individuality.
The human body is also a common theme in Whitman's poetry. Here, it forms the crucial link that connects each individual self to the communal Democratic self. At the same time, the body is inextricably tied to Whitman's image of the soul. He believes that without the physical body, there is no soul. This is because the human body is the vessel through which the soul interacts with and experiences the world. Therefore, in Whitman's poetry, the human body is sacred and every individual human is divine.
Whitman goes on to introduce the theme of gender, specifying that he treats men and women equally in his poems. "The Female equally with the Male I sing," he declares. Whitman considers the woman equal to the man because his view of gender is tied to his definition of the soul. To Whitman, women are just as sacred as men because despite their physical differences, they are all human (and souls are free from gender). In later poems, particularly in "I Sing the Body Electric," Whitman delves deeper into his ideas about gender.