She uses three related words: pledge, plight, and oath. Each (can) mean a pledge (perhaps her devotion to God), and the repetition (though each time a different word) speaks to her continually needing to reaffirm it, either out of devotion or perhaps desperation? The last line “Will surely come again -” is not exactly a reassuring statement with the open ended punctuation.
Another unusual feature is in lines 2 and 3 when Death does not come for her (she is not called) – is this perhaps a punishment for not keeping the pledge? To go to the glory of heaven is seen as a reward because life is full of sin, yet she equates her continued existence with natural / nature imagery: “sainted Bee” (sainted be wordplay), “Daisy”, “hillside”, “Bobolink”, and “Blossom” (b alliteration: to be, I be, I continue to be as I am?).
And she ends with a reference to “Her”, perhaps the Blossom, but perhaps someone else, such as her spirit or the previous poem’s quiet fairy of the soul? Christian imagery would usually refer to the oath to Christ as being male: He, however she could be playing with the idea of the female quality of nature which reconciles her oath to Christ (male) with her current state of living (female).