What I find interesting here is that she is addressing her soul as if it is a separate entity with which she is struggling with. I imagine she was investigating why her soul sometimes does the right thing but then sometimes allows the “caucus” of “Imps” to have their way and lead her astray. She’s asking why can’t we be good all the time and why is it so hard to resist evil.
As is often the case with her poems, the key is usually in the first line, especially with a single word. In this case she uses the word “Wilt” to pull double-duty. At first glance “Wilt” is a contraction of ‘will it’, as in ‘will it [my soul] toss again’, but “Wilt” is also what happens to a flower as it withers. Imagine our souls as a single flower in a vase that if not well tended eventually starts to droop away from the sun. Emily compares her soul (and herself) to flowers in many poems, so it seems reasonable she is playing on this theme.
The next word that stands out is “toss”, and here we can think of it in a couple of ways. If we recall the poem “We lose – because we win” she talks about gamblers tossing their “dice” but coming up short. I compared this to the Roman soldier casting lots for Jesus’ garments, which is to say that though eternal salvation was right there on the cross before them, they chose instead to play a game of chance. In other words, the soldiers made a poor choice and that leads to another reading of the word “toss” to mean that she is exploring why her “Soul” isn’t always constant and tends to “Wilt” like an untended flower.
The second stanza reminds me of the old cartoon trope where an angel sits on one shoulder and a devil sits on the other as they try to convince the protagonist what the best course of action is. Here she compares this to politics in which the “Angels” and “Imps” are having an election for her “Soul”. And the adjectives she chooses to use are worth noting because the “Angles” in this poem are “breathless” as if they are silent and silently hoping she will do the right thing but the “Imps” are more active because they are “eager” as they “Raffle”. There is a sense that evil is far more industrious than good and that it is always working against the “Soul” like how nature works against the lone flower in a vase as it slumps towards the ground. The angels here “[linger]”, but the “Imps” are gathered in a “caucus” which recalls the noisy and messy process of electing a politician.
So something is on Emily’s mind and she seems to feel like she is caught in the middle of either making a good decision or making a poor one. Perhaps this is why she was in a bad mood in her previous poem, “Heart not so heavy as mine“?