There's a certain Slant of light
The poem opens with the idea of there being a certain slant of light in winter afternoons that "oppresses." It kind of feels like the seriousness associated with "Cathedral Tunes." The speaker then compares the light to a kind of "Heavenly Hurt" that leaves no scar. It's impossible to define exactly what the light is or what it's like. But the speaker says it's everywhere, an "affliction" of sorts, that is sent from the air. When the light arrives, the landscape seems to listen and everything kind of stands still. When the light goes, there's something "distant" about it, kind of like death.