This is Bécquer's ars poetica: an answer, in nine stanzas, to whoever says that poetry is finished. «No digáis que agotado su tesoro, / de asuntos falta, enmudeció la lira». So long as the waves break, so long as the sun kindles the clouds, so long as there is something science cannot explain, so long as two eyes meet and a heart desires — there will be poetry.
Bécquer defines it not by its subjects but by its source: poetry exists as long as mystery exists and the world has beauty that will not fit into a formula. Each stanza is a «so long as» piling up reasons, up to the close: «so long as a beautiful woman exists, there will be poetry!».
The verse is kept in Spanish. Translating it in passing would replace the work with a paraphrase of it.