And now I Foam to wheat, a glitter of seas. The child's cry
Melts in the wall. And I Am the arrow,
The dew that flies Suicidal, at one with the drive Into the red
Eye, the cauldron of morning.
These last few stanzas of the poem are so interconnected that we're gonna take 'em all on at once. Saddle up, guys.
In the previous stanza, our speaker has told us that she's found a way to let go of "dead hands, dead stringencies." She's letting go of her mundane life, and submitting to the experience of the wild ride on Ariel.
And now she's undertaking a serious transformation. She imagines herself as "foam" among the wheat fields she's traveling through. She's "a glitter of seas." The sea is a pretty feminized metaphor—throughout all kinds of literature, the sea has been associated with the cycles of the female body. In this case, the speaker's letting go of her actual body, and imagining herself as becoming one with nature—with the sea, and also, with Ariel.
Then, she tells us that the "child's cry / Melts in the wall." Whose child is she talking about exactly? Is our speaker a mother?
Possibly. Is she talking about her own, childlike cry of fear and terror? That's also possible.
Whatever the answer to these questions is, we know that the speaker's connections to the human world are "melt[ing]," even disappearing. The experience of riding on Ariel is overtaking her, and her connections to the human world, her fears of Ariel's wild nature are dissolving.
The last six lines of the poem form a wonderful, overwhelming, intense conclusion to the poem. The speaker says that "And I / Am the arrow, / The dew that flies Suicidal." Did you hear that awesome slant rhyme of "arrow" and "suicidal"? Subtly, these lines are brought closer together, though not in perfect sonic harmony.
But what do these words actually mean? Well, we now know that the speaker has shed her human connections. In these last lines, it seems like she's become one with Ariel, who is galloping with intense and focused speed.
The metaphors here are deep and layered; the speaker is so closely intertwined with Ariel that it's as if the two of them together are the arrow, galloping with determined intent. And galloping how? Well, suicidally. (This is a Plath poem, after all).
Is the speaker talking about actual suicide here? Probably not. She may be on a wild ride, but she doesn't seem to be planning on throwing herself from the galloping horse. Instead, she's using the word "suicidal" more metaphorically. She's talking about extinguishing her sense of self. She's no longer the self she was at the beginning of the poem, riding on her horse with "dead hands." Instead, she's the arrow, Ariel herself. (Notice how similar "arrow" and "Ariel sound"?) She's merged with the horse.
Our speaker tells us that she is "at one" with "the drive" (Ariel's drive, meaning both her galloping and her instinct). And what's that red eye? Well, it sure reminds us of the red, rising sun. The poem begins in the early morning "substanceless blue," and ends with the speaker riding into flaming sunrise.
And let's be sure to note that this is not a happy, yellow sun. Plath describes it as a "cauldron of morning," which has distinctly witchy undertones. (Macbeth, anyone?) And we can't help but hear the word "mourning" in this last line too, which doubles the dark feeling that we're getting here.
All in all, this is an amazingly powerful image. It's an image of power, of control, of speed, of life and death all jumbled up.
The speaker has shed her human skin (metaphorically, of course), and she's become one with her powerful, galloping horse.
She's an arrow heading towards the bullseye of the sun. She "flies," "at one with the drive" (notice how the assonance of the long I sound there helps support her idea of oneness) and she's now all instinct, all power.
In the end, the poem's about learning to let go, and finding power in that kind of release. Pretty intense, ain't it? "Ariel" simultaneously makes us crave, and fear, a wild ride on a horse like Ariel.