There are multiple feelings expressed in Sylvia Plath's poem "Edge."
The first stanza of the poem states, very blatantly, that a women can only possess perfection through death.
The woman is perfected. Her deadWhile the second line of the stanza continues in the second stanza, it is certain that Plath made this a conscious divide. She is making a very straightforward statement: a dead woman is perfect. (Sorry, I am not sure why this jumped over in the text field.) A reader can see the main theme of the poem through the repetition of words which depict death: dead, bare, empty, stiffens, and odors. Plath simply feels as if death is the only option for her to feel free and accomplished. Therefore, the feelings expressed in the poem are ones which heavily conflict with each other: depression and happiness. What is meant by this is that, according to Plath, one cannot escape depression, and find happiness, until they are dead.
While I think we can assume that this poem does express its author's feelings about (and attitudes to) life, death and possibly betrayal, I would suggest a small caveat. When writers -even ones as 'confessional' and personal as Plath - write about death, suicide, despair and so on, they have a pen in their hand or a keyboard at their fingertips, not, say, a knife or a bottle of poison. Plath in particular creates highly theatrical pieces which may indeed reveal a lot about the writer, but which are nevertheless crafted and detached, and in many poems she seems to have enjoyed death imagery.
Perhaps this, in fact, is where we should begin: in 'Edge' Plath's feelings and attitudes seem to be very much concerned with images, a tableau, moreover one which is a little shocking. Only the title 'Edge' might suggest something of her actual feelings, since the poem itself is not concerned with someone on the edge of anything. Rather, we have a static image of death, an actual image: a statue or death-effigy. And an ancient statue - after a suggestion of Greek tragedy 'a Greek necessity' (suicide - see the myth of Medea, who killed her children) in line 4, this is confirmed when we read that the statue wears a toga. Nevertheless, at the same time we have 'her dead body', and an illusion of a Greek necessity - so corpse, or statue? (And whose illusion, the woman's or that suggested to onlookers?) The poem runs both ideas sumultaneously, and the two things share common properties: stillness, stiffness, lifelessness - except of course that a statue has never lived, only represented someone who has.
The statue's breasts are 'pitchers', another suggestion of stone, but 'now empty' suggests recent death, something that has lived and was once full. The babies are dead, too - but they are 'coiled serpents', and 'white' - again, we have corpses, and marble, and something else: 'serpents' suggest threat, but dead serpents are no threat at all. Another set of metaphorical images is introduced with 'petals' - roses and the garden, 'stiffened' in the night-time, the night flowers exuding odours; but these odours 'bleed', and we are back with the image of a corpse beginning to stiffen, decay and seep.
With the moon, the focus of the poem changes, pulls back from the close-up, as does the language, from the highly-charged and poetic imagery of the garden, the roses, to a prosaic 'nothing to be sad about...she is used to this sort of thing', as if the moon is an onlooker, one that may represent the human witnesses the writer imagines regarding her own death. Consider the tiredness and resignation in 'this sort of thing' - after the grandeur, death is just another of those ordinary things. The moon suggests the universe on a far greater scale than the merely personal, in which one death among millions matters nothing, yet Plath personifies 'her', whose 'blacks crackle and drag', casting the moon as one of those figures at funerals who attend but do not mourn. Is this (if anything is) Plath's sense of betrayal - that (her) death is/would be insignificant?