lost he may be in his life, and as the collective life of mankind goes on every individual "may contribute a verse" to the larger story that is mankind. 

What is the universal theme then? Life is its own value, its own prize and explanation.  

The essential idea is that no matter how miserable the world seems (cities filled with the foolish) and no matter how disappointed you are with yourself (of myself forever reproaching myself), and despite the seemingly futile struggle (poor results of all), life is still worth living. By the end of the first stanza, the speaker is in complete despair. O me o life is similar to Hamlet’s “to be or not to be” speech. The question is “what is the point of living if everything seems so terrible.”

The answer is a very concise way of stating the point or the meaning of life which is life itself. That sounds tautological (redundant) but that is the point. Even in the darkest hour, at the bleakest times in history, life still exists and history goes on. There is hope in that basic certainty. This poem is a celebration of life itself; at the same time, it suggests that struggle is a part of life and there is meaning to be found through struggle and that simply by being alive, you have inherent power and potential to contribute to the history of your and all (universal) life.

"O Me! O Life!" is part of Walt Whitman's collection of poems Leaves of Grass.  In "O Me! O life!" Whitman raises an existential question: "What good" can be found in life amid "the endless trains of the faithless" and the "cities fill'd with the foolish"?

The primary poetic technique that Whitman uses in this poem is anaphora: the repetition of the same word or phrase at the beginning of successive clauses or verses.   The bulk of the poem consists of phrases that begin with the word "of":

Of the endless trains of the faithless, of cities fill'd with the foolish,
Of myself forever reproaching myself, (for who more foolish than I,
    and who more faithless?)
Of eyes that vainly crave the light, of the objects mean, of the
    struggle ever renew'd,
Of the poor results of all, of the plodding and sordid crowds I see
    around me,
Of the empty and useless years of the rest, with the rest me intertwined

Another technique Whitman uses is alliteration--the repetition of initial consonant sounds.  In lines 2-4, for example, Whitman uses 7 words that start with the letter f: faithless, fill'd, foolish, forever, for, foolish, faithless.  From line 7 to the end of the poem, 4 words start with the letter p: poor, plodding, powerful, play.  It is interesting to note that powerful and play are nearly the opposites of poor and plodding. 

In his poem “O Me! O Life!,” Walt Whitman uses a variety of rhetorical devices including hyperbole, metaphor, imagery, symbolism, repetition, and rhetorical questions. Let's look at these in more detail.

Rhetorical devices are designed to draw readers into an argument or an emotional state and guide them to accept what the writer is saying. Whitman does this throughout the poem. He uses hyperbole, for instance, when he identifies the “endless trains of the faithless.” This is an exaggeration, but it serves its purpose of heightening readers' awareness.

Imagery fills the poem as we are invited to picture “the plodding and sordid crowds,” and the light symbolizes the knowledge and insight the speaker craves but cannot find. In his frustration, he repeats his exclamations, drawing his readers into his frustration and near despair. He also repeats the word “question” and then asks some rhetorical questions about life and its meaning and his own foolishness. Readers are to ask these, too.

The poet, however, provides an answer to his questions. He exists. He has life and identity, and he has something to communicate to the world.

In the first part of the poem, the speaker questions the meaning of life, wondering what good his own life does amid all the foolishness and emptiness he sees. In a series of anaphoras, lines beginning with the same word, "of," he catalogues the problems he perceives, weaving together the outward struggles of others with his own internal doubts. For example, he notes that cities are filled with the "faithless" and "foolish," then describes himself as also both faithless and foolish.

He wonders about the "plodding and sordid" crowds he sees around him in late nineteenth-century cities but says, in a typically Whitmanesque move, that "with the rest me [I am] intertwined," understanding that he is no different from what he critiques but is part of a larger, universal self that encompasses both the good and the bad. He ends the stanza by lamenting that he keeps asking himself over and over the "sad" question "What good amid these, O me, O life?" By this he means, how can he do good amid all the suffering he sees?

In the second, shorter stanza, the speaker gets the "answer": he matters because he is here and part of a "powerful play," the drama of life. Because he exists and has life, he has the opportunity to contribute a "verse" to the larger whole.

In sum, the speaker despairs of what he sees in the people around him and in himself, acknowledging his interconnectedness to those suffering around him. However, he overcomes his despair by realizing, optimistically, that he has a part to play in life because he exists and can contribute his gifts.