Repetition is crucial to the structure of the poem. The phrases "Do not weep" and "war is kind" are repeated five times in just 26 lines, including as a refrain at the end of the first, third, and fifth stanzas. This repetition has an unsettling, excessive, insistent quality. It's as if the speaker is trying to pressure or hypnotize the grieving family—or the reader—into believing an obviously false claim that "war is kind." And yet, that claim doesn't become any more true with repetition: in fact, it only becomes more absurd in the context of the poem, as the speaker reveals more of war's cruelties.
Repetition governs the rest of the poem, too. The poem repeatedly addresses the dead soldier's loved ones (stanzas 1, 3, 5) and the ceremonial gear of his regiment (stanzas 2 and 4). It repeatedly offers questionable "evidence" of war's kindness (lines 2-3 and 13-14). It repeats the line "These men were born to drill and die" (lines 8, 19) verbatim, and its rhyming line (11, 22) almost verbatim. As a recurring line at the end of a stanza, "[And] a field where a thousand corpses lie" becomes a second refrain.
These repetitions help to organize what is, rhythmically speaking, an experiment in free verse. The poem doesn't follow a strict meter, but otherwise, it's highly structured. The combination of predictable and unpredictable elements, order and disorder, may be meant to reflect the subject of war: a disciplined activity that results in the chaos of mass death.
Finally, a special kind of repetition, called diacope, occurs in line 10, as the word "great" repeats with only a few words in between. Here, diacope helps signal the verbal irony of the line: it's as if the speaker is sarcastically describing the god of war as, "Great, just great." (Alternatively, if the speaker believes what they're saying but the poet knows better, the repetition might be a sign of the speaker's excessive fervor for war.)