In this poem, Brooks employs musical devices, figurative language that evokes feeling through the use of certain repeated sounds, in order to emphasize a certain idea or word. For example, the word "We" appears at the end of every single line except the last one. This repetition is called refrain: when a poet repeats words, phrases, or lines as part of a pattern. In a sense, Brooks trains our ear to expect the "We" at the end of each line, and the final line feels more abrupt and cut short (as the lives of these young people are) as a result. (It is important that you read the poem with something of a pause after the "We" at the end of each line, as suggested by the line break, in order to hear this absence.)
Next, there is assonance (the repetition of vowel sounds) in the repetition of the long "e" sound in line 1: we, real, and we. There is consonance (the repetition of the final consonant sound) in the repetition of the "L" sound in lines 1-2: real, cool, school (also, cool and school rhyme). Left, Lurk, and late are alliterative (alliteration is the repetition of initial consonant sounds) due to the repetition of the "L" sound. "Strike straight" is also alliterative, especially if we combine with the next line's "Sing sin" ("S" sound). There is consonance in Lurk and Strike as well ("k" sound). On lines 5-6, sin and Thin and gin rhyme (and because Thin and gin are on the same line, they create internal rhyme). On line 7, "Jazz June" is alliterative ("J" sound), and on lines 7-8, "June" rhymes with "soon." Essentially, then, every word in the poem is connected to another word(s) near it except for the word "Die." In addition to the absence of the "We" at the end of the line, the word "Die" is further emphasized by its lack of musical connection to the words around it. This also helps to reinforce the finality of the meaning of the last line.