As the speaker attempts to describe what she went through, she uses anaphora and broader parallelism to create a feeling of relentlessness. Repeating the same words and sentence constructions again and again, she illustrates her struggle to precisely name or describe what she went to; she keeps turning to comparisons that can't quite capture it.
Take the anaphora of the phrase “It was not” in lines 1, 3, and 5. This anaphora emphasizes that the speaker can’t directly name what she experienced: she can only describe it through what it was not. The word “for” also repeats here, creating grammatical parallelism. This, in turn, shows the speaker is trying—and repeatedly failing—to work through what she experienced logically.
Anaphora appears again in stanzas 4 and 5, as the speaker starts three lines in a row with the word "And" (in what is also an instance of polysyndeton). Again, this repetition conveys that the speaker can’t describe what she went through in a totally straightforward way. Each comparison leads to yet another comparison, as she attempts to put words to this terrible feeling. Readers get the sense that the list of comparisons could go on and on—that the speaker could add "and" after "and"—without capturing what she truly felt.
The repetition of “and” also links the comparisons together. It implies that the speaker’s feeling encompassed all of these things: she felt like a sanded-down plane of wood, and like she was suffocating without a “key,” and like she was in a kind of perpetual “Midnight.” The use of anaphora, then, emphasizes just how terrible and also just how incomprehensible the speaker’s feeling was, since no single, isolated comparison can fully capture it.