What is the universal idea of "I Sing the Body Electric"?

I assume this question is asking about which universal themes are present in Whitman's "I Sing the Body Electric," or about how Whitman explores the universality of the body in this poem.
For some context, Whitman was a humanist, which means that he valued freedom and agency in human beings, both as individuals and as a collective. This poem (and other poems in Leaves of Grass) explores the physicality and the sacred qualities of being a human being. Whitman tells us in part 8, "If any thing is sacred the human body is sacred..." 
One universal idea in "I Sing the Body Electric" is the idea that all bodies are equal. Through his use of lists and catalogues throughout the poem, Whitman places descriptions of many different kinds of bodies side by side. In listing these different bodies, he gives them all equal value and attention. After describing the female form, Whitman writes in part 6, "The male is not less the soul nor more, he too is in his place, / He too is all qualities, he is action and power..." He also tells us in part 6, "The man’s body is sacred and the woman’s body is sacred, / No matter who it is, it is sacred...." Whitman believes that male and female bodies are equally important. Other bodies that Whitman explores are those of farmers and of slaves, as well as the speaker's own body. He repeatedly emphasizes that these bodies are equal.
Another universal idea present in the poem is the idea that human bodies refuse neat categorization or labels. In part 2, Whitman writes: "The love of the body of man or woman balks account, the body itself balks account, / That of the male is perfect, and that of the female is perfect." Thus, Whitman tells us that even though he's about to describe the physical body, he understands, and we should understand, too, that the human body resists categorization. Whitman implies that sometimes we are unable to use language to truly capture the human body in its entirety.