This poem sounds like a meditation that the speaker might say quietly to himself while he's waiting, a meditation that he might write down in his journal, or maybe to his family back home. Whoever may have read it, they (like us) would have noticed that this is a very, very repetitive poem. Anaphora is all over the place here (lines 3-4, 5-6, and 9-10), and so is alliteration (the beginning L sounds in "leave," "law," "lonely," for example). Toss into the mix the strict rhyme scheme (ABAB CDCD EFEF GHGH), and the repetition of certain words and phrase ("clouds," "waste of breath") and you have a poem that is even more repetitive than a children's song.
So, the poem says the same things and uses the same sounds over and over. So what? Well, did you notice how certain the speaker is that he will die? It's not just a given, it's a guarantee. The sounds and words in this poem are guaranteed to repeat themselves, too. The rhyme, the meter, the anaphora, the alliteration—it's almost like we know what's coming next. We can almost predict the poem's sound. On a sonic level, the poem's constant repetition illustrates, reflects, mimics the speaker's absolute belief that he will die. It's a bummer, but a cool-sounding bummer nonetheless.