We think the speaker of this poem sounds like he's trying to impress a crowd. He would be right at home at a circus or a magic show. He could even be a con artist, performing card tricks on the street. He knows he has to draw his audience in right away, and make his pitch fascinating.
The speaker doesn't waste any time because he doesn't want to lose us. His descriptions are fast and dramatic at first. He paints a picture that enchants us and pulls us in. Once he's got us, he can slow his patter down, or speed it up as he sees fit. He can tell us about his strange visions, but he's always careful to add some verbal fireworks. He repeats himself for dramatic effect ("That sunny dome, those caves of ice!" [line 47]), just like you would if you were preaching, entertaining, or trying to sell something to a crowd. He's confident, even a little showy, but he's also got one eye on the crowd, making sure we're with him. He never lets the energy drop.