There's a certain Slant of light
Winter Afternoons –
That oppresses, like the Heft
Of Cathedral Tunes –
Heavenly Hurt, it gives us –
We can find no scar
But internal difference
Where the Meanings, are –
None may teach it – Any –
'Tis the Seal Despair –
An imperial affliction
Sent us of the Air –
When it comes, the Landscape listens –
Shadows – hold their breath –
When it goes, 'tis like the Distance
On the look of Death –
The speaker states “When” and not “if”, implying inevitability. It also implies universality; the broken seal and affliction is send through the “Air” and the “Landscape” also responds. It suggests a sort of negative  Pantheism , affliction that permeates the natural world, just as God lives in nature in a positive sense.
Theres a certain Slant of light