The impact of Keats's repetition of the word what is that he wants to express the thoughts of the people on the urn. In this way, it will be easier to understand what the people are trying to mean with the urn.
Alliteration focuses readers attention on a particular section of text. Alliterative sounds create rhythm and mood and can have particular connotations. For example, repetition of the "s" sound often suggests a snake-like quality, implying slyness and danger.
