Since then – 'tis Centuries – and yet Feels shorter than the Day
Wait a minute – this happened centuries ago?! This really throws a wrench in the whole system.
The poem seems to be telling a recent memory, but this all actually happened a really long time ago. Meaning...yep, the speaker has been dead the whole time. Interesting.
"Feels shorter than the Day" is just an old-fashioned way of saying something like, "feels like just yesterday." So this memory remains vivid for the speaker.
I first surmised the Horses' Heads Were toward Eternity –
These final lines recall the very first time the speaker encountered the horse-drawn carriage and had a feeling that they were more than just regular horses – that they signified her journey to the afterlife.
Ending on the image of the horse heads is really smart of Dickinson, because they jut forward and it almost looks like they're pointing toward something. In this case, "Eternity."
It's also very bold of Dickinson to end on this image because this is the first we've heard of the horses, and suddenly she's asking them to hold up the most important moment of the poem.
The final stanza is full of surprising moments for the reader. We find out the speaker has been dead for years and we're introduced to (and left with) this striking image of the horses' heads pushing forward.