Healthy Dose of Heroic Couplets
A cliché in cooking is that folks eat with their eyes first. In other words, they take in how their food looks first, before diving in to taste it. The same could be said of poetry. Readers, of course, read with their eyes first, second, and, well, always. Still, there's something about the way a poem sits on a page—the overall impression of its form—that creates a first impression.
In the case of "The Tuft of Flowers," that form is pretty evident. The poem is arranged neatly into self-contained, rhymed couplets, or two-line pairs. Looking more closely—or listening more closely—we find out that these couplets have more in common that just being close to one another.
In fact, they all share the same meter. That is, each line contains five iambs—two-syllable pairs in which the first syllable is unstressed, and the second one is stressed. The rhythmic beat of an iamb sounds like "daDUM," and you can hear five of those bad boys in any one of the poem's lines. For example:
And feel a spirit kindred to my own; (35)
If you were to read that line out loud (and you totally should), you'd hear a pattern: daDUM, daDUM, daDUM, daDUM, daDUM. You can try this for pretty much any line in this poem, and that pattern will hold up.
Now, five iambs in a single line means that we have a metrical pattern known as iambic pentameter (penta- meaning five). What's more, when you get a rhymed couplet that also happens to be written in iambic pentameter, then you get a super-deluxe, rare poetic occurrence known as the heroic couplet. Nifty, eh?
We'd say so. You see, heroic couplets are an old form of poetry that was used for describing the dashing exploits of bold heroes. In the case of "The Tuft of Flowers," though, we have a dude...standing in a field with a butterfly and some flowers. The speaker's not exactly the poster boy for heroic action, so why did Frost go with this form?
Well, if you consider that this poem makes a point about the interconnectedness of all humanity, then we'd say couplets are a pretty apt choice. Every line in this poem has a buddy, much like the speaker and the mower. They may not be in close contact with one another, but the speaker realizes—thanks to the leftover flowers—that he and the mower share a profound and special connection.
In the same way, the lines of this poem are connected in the most poetically-special way possible. Ultimately, only heroic couplets can do justice to the level of connection that the speaker finds out there in that field.