The speaker could be Frost himself, but that's always a dangerous assumption, Shmoopers. Just because you see "I" doesn't mean that we're looking at a diary entry. Whoever the speaker is, we know that he or she wants us to know that these musings are grounded in the speaker's reality. Whoever this is came upon this situation with the spider, moth and flower. It isn't some thought experiment. Even though the poem wanders off into all sorts of natural and philosophical territories, the first word of the poem draws our attention to the speaker's personal experience: "I."
Knowing that this poem is told from a personal perspective allows us to be more okay with all the ambiguity we get later on. If this poem was spoken from a more omniscient or third-person point of view, we might be itching for more resolution. (Come on, speaker, less questions, more answers.) Instead, we follow it from a personal recollection of a specific situation and then through an increasingly more intense series of questions. That's okay, though. We're not beaten over the head by this speaker. We feel comfortable with these tough ideas because we know that the speaker is just as lost as we are—he's trying to figure it all out, too.