Relevance theory and poetic effects

Why should poets choose to repeat concrete sounds or abstract structures when conveying their poetic messages? After all, it would seem that repetition tends to slow down comprehension and require greater cognitive effort. The key to understanding the rationale behind these poetic devices is the communicative principle of relevance proposed by Sperber and Wilson: interlocutors communicate on the assumption that what is being said is relevant in the communicative context. But how things are said is also relevant: poets create patterns for pragmatic, communicative reasons. Poetic devices also promote affective states, which cannot be reduced to cognitive ones.