The metephor is about our spiritual journey.
What is killed in this metephor is the person feeding off thier spiritual potential, as they have not become alive in the spirit. In the material world both the host and parasitic plant die.
So in the metephor the host is our spiritual potential that is being fed off, but without connection to the source of that potential, that potential dies and so does the one feeding off it. (Let the dead bury the dead)
God is just, compassionate, all merciful and forgiving. Thus we are all judged as such, nature, nurture and our given chances are all written on Tablets of Chrysolite.
It is hard for is to submit, to become a willing slave/servant, a lifelong journey for most of us.
What is of interest to me is those that were given a great spiritual station, were lighted by faith, burnt like a bright light and then went, all is a short existence.
This story may interest you.
Thomas Breakwell
Regards Tony