This poem focuses only on the effect of a certain kind of light that the speaker notices on winter afternoons. It quickly becomes clear that this is not going to be a poem extolling nature or winter light’s virtues, for this light “oppresses.”
What kind of oppression this is, exactly, is what the rest of the poem describes. In the first stanza it is described as “like the Heft/Of Cathedral Tunes –,“ which is not a common simile for something oppressive, making it clear that this light’s oppression is of a complicated nature.
This slant of light gives a “Heavenly Hurt” to the observer of it—that is, something that causes no outwardly visible damage (“We can find no scar”), but instead causes a mental or spiritual change (“But internal difference, / Where the Meanings, are –“).
This change cannot be induced through teaching (“None may teach it – Any –“); instead, it must be experienced. Though it is “Despair,” it is an “imperial affliction,” that is, a regal or royal affliction, that although painful, leads to an uplifting.
It is powerful enough that even nature notices its presence (“When it comes, the Landscape listens –“), and its departure allows for a preternatural understanding of death (“When it goes, ‘tis like the Distance / On the look of Death –“).
This poem very closely describes a fairly common theme of Dickinson’s—that of change as a fearful but illuminating process, both painful and essential. Here this awe of change is embodied in the “certain Slant of light” that becomes the place of departure for the transformation. This slant of light is oppressive, but this is no simple, purely negative oppression, it is instead oppressive like “the Heft/Of Cathedral Tunes –.”
The choice of “heft” here, instead of “weight,” which would actually have fit the rhyme scheme more closely, emphasizes the paradoxically uplifting aspect of this oppression, because while “weight” gives the reader solely an image of a downward force, “heft” implies a movement upward, albeit a difficult one. Thus while this slant of light is oppressive, while it creates difficulty for the speaker, the diction makes it clear that it is also uplifting.
This makes the surprising use of the simile of the “Cathedral Tunes” more understandable, as this seems to fit in with Dickinson’s views of religion. Faith, religion, and God are not easy for her; instead, they have a great difficulty, an oppressiveness, about them, and they cause “Heavenly hurt”—the importance of the adjective here is emphasized in the alliteration, and the flipped syntax of the line, opening with the direct object instead of the subject. This difficulty is, however, one that leads to greater understanding, and thus perhaps uplifts her, and in so doing takes her closer to God.
The importance of this painful transformation becomes even clearer in the third stanza. Here we see that its lessons cannot be taught, but must be lived; the emphasis of “Any” at the end of the first line of this stanza makes this very clear. And it is a “Seal of Despair – / An imperial affliction.” The close proximity of “Seal” and “imperial” make this experience into something that brings she who experiences it onto another level -- into a select, almost royal group of those marked by it.
This painful transformation has a better side to it implied throughout the poem, a certain uplifting that makes it worthwhile, that makes those who have lived through it members of a select club. However, the final stanza ends this transformation, and in so doing, leaves the day much closer to ending and the observer much closer to death, the word with which the poem itself closes. Yet death is balanced closely with life, as is shown by the fact that “death” rhymes with “breath,” an obvious symbol for life, earlier in the stanza, so even this death is not purely negative.