Repetition is one of the oldest poetic techniques; think of chanting or the King James Version of the Bible, which includes memorable passages of lyrical repetition. "Begats" and "blesseds" pepper the verses, from Old Testament genealogies to the New Testament’s Sermon on the Mount. Repetition in poetry can carry the same meditative or incantatory effect, as though the poet were speaking to something larger, more ancient and perhaps more sacred than himself.
Some forms of repetition can create tension within a poem, offering a sense that the work is picking up momentum, gradually barreling toward something big—an idea, a confession, a harsh or wonderful truth. Often this sort of repetition mimics a mind in the grip of obsession, insanity or a loss of control. Consider how we repeat to ourselves "Yes! Yes! Yes!" upon hearing good news, or "Go! Go! Go!" when the team we are rooting for is winning the game.
Repetition is frequently seen at the end of a poem. In these cases, it is used not as a means to torque and intensify the poem, but as a form of closure. A line might be repeated in its entirety two or three times in order to slowly lull the poem to its end or help it "hit the brakes." For example, Robert Frost ends his powerful poem "Stopping by Woods on a Snowy Evening" with the lines: "And miles to go before I sleep, / And miles to go before I sleep."
Poetic forms that mimic song lyrics, such as blues poetry, use repeated lines as touchstones, reminding readers of what the poet wants to convey most. Repeated lines that appear in clusters, sometimes called "refrains," are usually a product of a poet writing by ear. Here, the sound, the beat, sustain the reader and give the poem support, as though it were held up by the “columns” of repeated phrases.
There are many more poetic forms—including villanelles, sestinas, pantoums—in which repetition of words, phrases or entire lines is key to the poem's construction. However, even if repetition consists only of a word or two, most poets work to ensure that the use of the repeated fragment never means the same thing twice. By reexamining what is being repeated, coming back to it time after time, readers notice how the poem quietly grows and changes.