The approach of death is, well, frightening. We bet that for every movie you can name that doesn't have the threat of death as the main source of tension and fear, we can name ten that do. What we're trying to say is that fear of death is pretty universal. Living things tend to have an aversion to death right? That's part of how we stay alive. Still, it's worth noting that this line does not try and crank up our fear to the boiling point. It's a fairly calm and contemplative entrance to the idea of the moment of death. But it definitely undoes the latch and lets fear into the room.
like the hungry bear in autumn (line 2)
OK, we don't want any kind of bear to come at us, much less a hungry bear trying to stock up before winter. More than anything else this image suggests the implacability of death. Bears are big. There's not much you can do to stop a bear that's coming at you. It's a way for our speaker to say: death is coming, and it's not going to be stopped.
like the measle-pox (line 6)
If we thought things couldn't get any scarier, now we have all the suffering of a long drawn out disease to consider. Our speaker is giving us a variety of images and comparisons. Death is a complicated thing, it seems, capable of coming in many ways.
like an iceberg between the shoulder blades (line 8)
This imagining of death is almost the sensation of fear, that shiver down our spine. Ever heard the expression of an 'icy feeling of dread'?
I want to step through the door full of curiosity" (line 9)
This is the pivot, the turning away from fear. Our speaker is announcing that despite all that we might normally be terrified about, she will not be afraid. She chooses instead to be curious, to be open to amazement that is available if you step out from under the fear.
I don't want to find myself sighing and frightened (line 26)
Now our speaker makes it even more clear that it is her intention to take a path that leads away from fear. There's the sense that, as well as not being much help, the fear would be a waste, getting in the way of the possibilities and wonder that might exist beyond this life.