Why does a loaf of bread seem like a hill to the fly in "The Fly"?

In "The Fly" by Walter de la Mare, the speaker tries to look at the world from the perspective of a fly, which is a tiny creature compared to a human.
The speaker notes that to a fly, a rose must seem as a feather bed would to us and a dew-drop like a mirror ("looking-glass"). He then continues to make other comparisons. Finally, at the beginning of stanza three, he imagines that to a fly, a loaf of bread must appear like a "lofty hill." That is because a loaf of bread is so much bigger than a fly. We can envision a fly landing on a kitchen table and peering up at the bread, seeing it rising seemingly endlessly into the sky.
The poem plays with point of view, urging the reader to think about how the world appears to creatures who are not us. The more we can look at life through others' eyes, the more we build empathy.