Lines 1-6 Summary

Get out the microscope, because we’re going through this poem line-by-line.

At times poetry is the vertigo of bodies and the vertigo of speech and the vertigo of death;

In this opening line the speaker uses a metaphor, that feeling of not knowing which way is up or down that some people get when they get onto the roof of a tall building.
The repetition of "the vertigo" three times at the beginning of each clause is an example of anaphora, and is almost dizzying itself!
And that overuse of "and"? In the poetry biz, that's something called polysendeton, where authors use conjunctions (like "and" or "but") repeatedly in the same sentence, usually unnecessarily. Here it gives the line an improvised feeling, as if the speaker were just thinking out loud, not editing and censoring himself.

the walk with eyes closed along the edge of the cliff, and the verbena in submarine gardens;

We're still talking about poetry here, and the dizziness continues! The speaker compares poetry to walking blindly along a cliff, and to the herb verbena in underwater gardens.
The first part of the line is an extension of the metaphor begun in the first line, which compares poetry to vertigo. Watch your step! If there's anything that could give a Shmooper vertigo, it's walking with eyes closed along the edge of the cliff.
The metaphor shifts, however, in the second clause. Here we go from vertigo to verbena. This herb is sometimes said to have divine powers, but it sure doesn't grow underwater. The idea of this magical flower growing below the sea is an example of surrealism, a literary movement from the twentieth century that emphasized the importance of dreams and dreamlike images.

the laughter that sets on fire the rules and the holy commandments;

Jinkies! This metaphor is slippery! It's gone from vertigo to verbena, and now it's comparing poetry to laughter—but not just any laughter. This is the rebellious kind of laughter you use when you're about to do something that is against the rules.
Poetry is rebellion, according to this line. How could that be so? Is it because of "poetic license," which allows poets to creatively bend the rules of grammar?
An example of this can be found right in this line, in fact. Wouldn't it be more natural to say, "that sets the rules and the holy commandments on fire"? The line inverts the natural word order of English, and breaks the rules of syntax using a poetic device called anastrophe, the inversion of the expected word order (beeteedubs—Yoda was really good at this, or should we say: good at this, Yoda was?).
This line is especially cool because it doesn't just describe poetry's rule breaking; it demonstrates it!

the descent of parachuting words onto the sands of the page;

And, surprise, surprise, we get another metaphor for poetry. Now poetry is described as a parachutist and the empty page as a desert where it lands. This is an example of personification, because poetry becomes the little dude jumping out of the plane.
What kind of image does this metaphor give us of the poet's work? It sounds almost random, just falling lazily out of the sky, rather than hard, deliberate work. This, combined with the conversational opening line gives the poem a spontaneous feel.
The surrealists, by the way, were big fans of randomness, and would sometimes juxtapose strange, unexpected, or random images and objects together.
Check out the "Shout-Outs" section to find out about another poet who was into parachutes.

the despair that boards a paper boat and crosses,
for forty nights and forty days, the night-sorrow sea and the day-sorrow desert;

Here poetry becomes despair, but it is a personified despair. This despair jumps on a little paper boat and crosses the sea and the… wait, a minute… the desert? More surrealist madness, folks! These images could come from a dream, right? Often the surrealists would use their dreams as inspiration for their art.
This comparison of poetry and despair here makes it seem like despair is the motivation for the art. It isn't a depressed despair that just wants to stay under the covers and eat chocolate ice cream all day, though. It's a desperate despair that boards a ship and takes off to cross the sorrow and leave it behind. In a way, that is what poetry does—it puts our pain or despair into words.
The reference to forty nights and forty days could be to Noah, who built an ark and floated in the rain for forty days and nights, or to Jesus, who went out into the desert for forty days and nights to fast and be tempted by the devil. (See "Shout-Outs" for more on that.)
And while we're talking about forty days and nights in the sea and the desert, check out those neologisms that Paz invented by hyphenating night- and day- and sorrow. These new adjectives give the line a sing-songy rhythm, and also add to the dreaminess of the imagery. (For more on things like rhythm and structure, go check out our "Form and Meter" section.)