This poem reads more like a play than a typical poem. It's chock full of dialogue, which sounds like, well, people talking. And these people talk, for the most part, just as real people would talk. We could easily believe that this is a really marriage, and it's really falling apart.
Still, the language of the poem has its poetic points. Check out lines 79-80:
"Making the gravel leap and leap in air,
Leap up, like that, like that, and land so lightly"
These lines show how this poem is realistic and poetic at the same time. We can sense the woman's frustration, and almost see her physically mimicking her husband when she says "like that, like that." Plus, the alliteration of the letter "l" in this line screams poetry, not prose. Frost is using those sounds to demonstrate the lightness this woman saw her husband digging with, and to linger over the frustration she feels that her husband isn't grieving more—like she is. To make a long story short, she lilts her way to a meltdown.
Throughout the poem, there are moments like this where the poet peeks through the realism of the lines. Or, perhaps, this poem is merely pointing out that there is poetry in everyday speech. Either way, it's important to remember that this poem is both a poem and a dialogue, which means it sounds like both at once.