I haven’t read Dracula, but I’ve seen from your comments that you need to figure out a meaning for school.
The cool thing is, there is no wrong answer.
Your idea of it being about purity / sin / change etc. - you said you got confused using this metaphor because when you categorised people as ‘good’ and ‘bad’, they still ended up facing the same fate. That could be a metaphor all on it’s own.
You could write about how Stoker was trying to say that change happens in life wether you’re ready to embrace it or not and no matter how good and pure, or bad and impure someone is, everyone faces the same fate (death). Dracula represents change and he comes for everyone and people react differently but their outcomes are seemingly unrelated to their reactions - just like life. So ultimately, you might as well strap in and embrace change because being happy in the moment is all that you can control.
I dunno. Like I said, I haven’t read the book, I’m giving that analysis just based on your post, but it seems vague enough that you could probably justify it without being contradicted?
I think you might have gone into this with a misunderstanding of who Sylvia Plath was.
You’re reading the journals of a woman with depression who eventually committed suicide. She isn’t ungrateful and lacking in foresight - she’s lacking in serotonin, dopamine and norepinephrine because depression is caused by a chemical imbalance in the brain.
What you’ve discovered is that depression sucks. That you can have caviar and champagne and all kinds of fun and you still feel horrific.