The leaves they were withering and sere; (line 3)
We don't find out about the death and grief that are at the heart of this poem until it's almost over. Still, from the very beginning, there are little things that foreshadow that theme. This image of the crispy brown leaves on the trees is definitely a representation of death. Check out the words he uses: "withering" and "sere." Like a lot of words in this poem, they sound like what they mean, and help to give a cold, shivery feeling to the opening lines.
And now, as the night was senescent (line 30)
Even the night is growing old and dying. Instead of just ending, the night passes away like a living being. When even things like the night start to die, it intensifies the feeling of sadness and loss that fills this poem. Between the skies and the leaves and the dying night, it feels like the whole world is passing away.
But were stopped by the door of a tomb (line 76)
Now we get into the really serious death imagery. So far, this poem has had nothing but natural things in it. All of a sudden, we run smack up against our first man-made object…which happens to be a tomb. Not a great sign. We were already thinking something bad was up, but now we start to piece together the details.