Our speaker imagines death approaching like a hungry bear. Actually she's even more specific: a hungry bear in fall. This is a pretty menacing image.
Mentioning "in autumn" seems to be a way to accentuate how hungry the bear is – in the fall bears are preparing to hibernate, so they're more desperate for food than usual because they need to put on enough weight to make it through the winter.
At the same time, there's a way that giving death an image like this, a physical form, makes death smaller, more manageable. A bear is something that we can know about and understand – at least from nature TV shows. Death, on the other hand, is something pretty mysterious.
Since the phrase starts with "When," we're waiting to see what happens when death comes.
The "When" also emphasizes the inevitability of death. She's not saying "If death comes," she's saying "When death comes." It might seem pretty obvious that we're all going to die, but the speaker really seems to be facing that fact instead of shying away from it.
when death comes and takes all the bright coins from his purse
Now our speaker re-imagines death as a person, a shopper. At least, we're pretty sure it's a whole new image, since most bears don't carry purses.
Those bright coins really stand out. They contrast with our preconceptions of death, which is normally associated with darkness.
By rephrasing or re-imagining the arrival of death, she's delaying the part where she follows up on that "when" which makes us even more curious.