Imagine, if you will, a freshly-mown country field. Grass is lying all over the place in ragtag piles, still wet from the morning dew. There, smack in the middle of it all, stands our speaker. That totally bummed-out expression on his face lets you know that he's contemplating the utter isolation of human existence.
As settings go, the natural world is a pretty appropriate choice for thinking about human isolation. This poem just wouldn't have the same effect if the speaker was feeling all alone in the middle of Times Square in New York. That's not to say that you can't feel lonely in a crowd, but the vastness of nature tends to underscore our sense of isolation (check out "Themes" for more on that).
At the same time, the natural setting also makes the speaker's discovery of connection all the more surprising and rewarding. He just happens to stumble onto a preserved bunch of flowers in the middle of a field and decides that the encounter must mean something. The flowers are a sign, a message: somebody was here, somebody saw these same flowers, and somebody decided to let them keep growing.
In the vastness of the natural world, then, out in the middle of a country field, the speaker finds undeniable proof of a human connection. Given his physical isolation (well apart from the butterfly, that is), this message seems all the more powerful.
Of course, there's a creepy side to realizing that, even alone in nature, you can never escape human contact. But our speaker's okay with that, if it means that he's not totally alone in the world. We're totally people people, Shmoopers, so we're okay with that too.