By the start of the second stanza, the speaker appears to be building upon some of the religious ideas we saw in the first stanza. We get a sort of paradox in line 5 that compares the light to a kind of "Heavenly Hurt." Heaven's not supposed to hurt, so we get the sense that the speaker is providing a contradiction between what heaven is supposed to be and what it appears to be here in line 5.
It's almost as if the speaker is giving us a bit of the sublime (heaven) and a bit of the earthly stuff (hurt) at the same time. And when we think about life and "light," we understand that we often get combos of the good with the bad. Sometimes the "light" can be pleasant, but sometimes it can be painful (think of light shining in your eyes).
Adding to the sublime kind of vibe we see here, line 6 tells us, "We can find no scar." So all the "Heavenly Hurt" from the slant of light doesn't leave any physical evidence behind. The "hurt" is more so internal and unable to be seen.
So the lack of physical evidence makes this "Slant of light" even more difficult to define or explain. All of the effects are internalized and are therefore understood or defined in a more personal way.
By now, we see how the speaker is using the natural image of winter light to illuminate some themes related to internal conflicts and despair. The "Slant of light" at this point is therefore a kind of extended metaphor for these personal struggles.
But internal difference— Where the Meanings, are—
Line 7 provides some more ideas related to the speaker's internal conflict by indicating a sort of "internal difference" that the slant of light illuminates.
So, although there isn't any physical evidence of "scars," there is some emotional or intellectual evidence of an "internal difference" within the speaker.
But what the heck does the speaker mean by all that? What's an "internal difference"? Since we're dealing with Dickinson, we can't expect many concrete answers. But based on what we've seen so far, the speaker appears to be pointing to issues of individual perception or "difference."
Line 8 makes sense to us then when we consider the problem of "Meanings." Meanings are largely based on perception, especially when we're dealing with intangible sorts of things like heaven, emotional pain, etc.
So the speaker is indicating here that all of these "Meanings" are located within us or in our "internal difference." In other words, they're not located in a dictionary with a neat little picture beside them.
But although the "Heavenly Hurt" is painful, it does appear to illuminate certain things like "Meanings" and the speaker's "internal difference." So it's not entirely bad since we'd all like to learn a few more "Meanings" when it comes to life and our internal conflicts.
By now we should talk a little bit about those dashes. We know Dickinson uses them a lot, and here they seem to act like a bridge between ideas. It's like we're meant to consider each line separately, but must then consider that same line in context with the line that comes after. In other words, the dashes seem to suggest that certain ideas are independent of one another but they're also part of a larger picture. Check out "Form and Meter" for more on those dashes.