The poem is called "Love Sonnet 17," and it comes from a book called 100 Love Sonnets, so naturally love is one of its major themes. The speaker contrasts his love for this woman with the love one feels for precious gems and beautiful flowers. Then he tries to define this love more concretely: it's like the love one has for "dark things;" it’s like an aroma; it involves some strange destruction of one’s individuality... hmmm, nothing seems like a perfect fit. Bottom line, love defies explanation. The speaker attempts to define love, but just like every attempt before him, he just can't do it.
True love defies explanation. Neruda knew this from the start; he wasn't trying to define love, he was trying to show that it can't be defined at all.
Neruda's love poem isn't very original. So we can't define love – what's the big deal? We want to see someone who can define it.