This two-stanza poem written in an open form compares the activity of a noiseless, patient spider to the activity of speaker's soul. Not only that both activities have many actual similarities, the speaker also uses alliteration and repetitions to enhance similar atmospheres in both stanzas.
In the first stanza, the speaker notices a spider that stands isolated on a little promontory. Even though in this case, the spider is most likely on some kind of branch, the speaker uses, "promontory," to show how big the world is from the spider's perspective. The speaker sees the spider's making web as a kind of attempts to explore the "vacant vast surrounding." The spider uses all of its energy to push out the filament from its small body. The repetitions of the word, "filament" emphasize this process that require both the strength and time. However, by "Ever unreeling them, ever tirelessly speeding them," we know that the spider never gives up but keeps trying more and more eagerly. Words like "unreeling" and "speeding" are hard to pronounce because we have to slow down a little to pronounce them clearly. I think the speaker again wants to emphasize that this is a very slow and tiring process.
In the beginning, the speaker is just looking at the activity of a spider without too much emotion. However, in the second stanza, by personifying his soul and by saying, "O my soul," more and more emotions pour in and out. There is a close affinity between the two stanzas. For example, "isolated," is similar to "detached," and "vacant vast surrounding" is similar to "measureless oceans of space." In addition, both the spider and his soul are seeking for the connections with the outside world. I think when the speaker sees the spider, a product of nature, at least he realizes that his soul is not the only one that is "ceaselessly musing, venturing, throwing, seeking the spheres to connect them," and he is not alone. Actually by looking at the spider, the speaker is already undergoing a process of connecting with nature.
The way that the speaker uses alliterations and makes the lines longer and longer provides the readers with a sense of powerlessness. Compared with this world, we are so tiny, and even if we keep trying, we never know if we can really achieve anything. I notice that the ends of both stanzas leave us big spaces to think. Notice that neither time nor place for them to find the connections with the outside world is mentioned. Moreover, we don't even know whether they still have to do the same thing over and over again if they finally succeed in forming bridges. I don't know how to word what I mean. I mean after a while a spider will recycle its filaments and make a web in another place. So if the soul is really like the spider, then it makes me tired even to think about it.