At the start of the poem, the speaker addresses a listener as "you." He explains that his love for the listener cannot be adequately compared to a rose made of salt, to topaz, or even to carnation flowers that produce fire. None of these metaphors are suitable, he claims, instead saying that his love can best be compared to the love people feel for obscure and mysterious things. This type of love comes from an unknown and private place, between his soul and his shadow. He next compares his love to a plant, but not to the colorful flowers he mentioned earlier. Rather, he says, it's like a plant that doesn't bloom. Instead, the plant holds the beauty of its flowers internally. The speaker compares himself to such a plant, saying that the listener's love has caused his body to carry the smell of the earth.
These first eight lines of the sonnet revolve around the speaker seeking out an object of comparison for his love. He seems to find it important, and even urgent, to use figurative language of some sort in order to tell his lover how he feels. He meets varying degrees of success during his search for comparisons. The first few that he tries out are entirely rejected: flowers and gemstones, apparently, aren't anything like the speaker's love. He seems to reject these similes because they are too cliche, dramatic, and exuberant. Instead, he suggests, his love is so intimate that it can only be expressed through quieter means. It exists "between the shadow and the soul"—two formless, invisible, and hazy things in and of themselves.
Yet even here, as he seeks a subtler expression of love, the speaker somewhat clumsily insists on using figurative language: he says that he loves his listener "as one loves certain obscure things." The insistence on figurative language in such a strange and convoluted sentence is striking and raises questions about the speaker's aims in this poem. Does he wish to find an outside object of comparison in order to contextualize and contain his feelings? Does he do so in order to obey the conventions of the love poem? Or is his insistence on metaphor, simile, and comparison a type of shyness in the face of his own emotions? Though there's no single clear answer, he carries on after this with yet more metaphorical comparisons.
The next comparison is in marked contrast to the roses and carnations of the first stanza, and the speaker finds this image more suitable. If his love is like a plant, he says, it's more like one that isn't in bloom. It's no less beautiful because it keeps its flowers hidden away—they still exist, the speaker argues, contained within the rest of the plant's body. Similarly, the speaker suggests, his own love is internal rather than loudly expressed. But that's not because he doesn't care. Instead, it's because his love is intimate and even exclusive. It's reserved, in other words, for the listener of the poem.
As the title announces, this poem is a sonnet. Though many contemporary poems play with the conventions of the sonnet form, rejecting some "rules" and embracing others (and though translation also alters certain poetic choices, especially concerning rhyme and meter), we can see in these first two stanzas that Neruda is largely sticking to the conventions of an Italian sonnet. In this form, the fourteen-line poem is split into three stanzas. The first two stanzas are each quatrains, consisting of four lines each. The final stanza is a sextet, consisting of six lines. Furthermore, in an Italian sonnet, a sudden shift occurs between the second quatrain and the concluding sestet. This shift might include changes in rhyme or meter, but it also usually brings a change in perspective, focus, or tone. We can already see this taking shape, because both of these two stanzas revolve around the speaker's search for an apt metaphor to describe his love. Going into the poem's final stanza, we can expect to see some type of change or twist, though it's not obvious what that will look like.