The poem has a really smooth, dreamy sound, almost like what you might hear if you happened to stumble upon Octavio Paz talking in his sleep. How does he get this effect? Repeat after us: repetition!
Just look at the first line:
At times poetry is the vertigo of bodies and the vertigo of speech and the vertigo of death.
All that repetition of "the vertigo of" over and over is called in the poetry biz anaphora. What's more, it sounds like a magician trying to hypnotize someone into thinking they're a chicken, or something… All those soft G's in "vertigo" and the repetitions of "the" over and over makes us feel ve-ry slee-py.
Another sound that adds to that sleepy sensation is the repeated S. There are shushing S's in just about every line. For one example, look at lines 4 and 5:
the descent of parachuting words onto the sands of the page;
the despair that boards a paper boat and crosses
Read out loud, those lines give us a whole heapin' helpin' of smooth and sleep S sounds to linger on. What's more, that poem's last one really whispers it on home. The repetition of the S sound throughout the poem is a technique called consonance, when a consonant sound is repeated.
So why all the sleepytime sounds there, Octavio? Given Paz's enthusiasm for surrealism (which relied on dreams as a vital source of imagery and a window into the unconscious), it seems only natural that he includes all these suave, soft sounds and repetition in his work. Even on a sonic level, this poem is encouraging a dream-like state to delve deeply into the hidden powers of poetry.